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  1. 25 5月, 2018 3 次提交
  3. 18 5月, 2018 2 次提交
  5. 14 5月, 2018 2 次提交
    • R
      sched/core: Distinguish between idle_cpu() calls based on desired effect,... · 943d355d
      由 Rohit Jain 提交于 
      sched/core: Distinguish between idle_cpu() calls based on desired effect, introduce available_idle_cpu()

In the following commit:

  247f2f6f ("sched/core: Don't schedule threads on pre-empted vCPUs")

... we distinguish between idle_cpu() when the vCPU is not running for
scheduling threads.

However, the idle_cpu() function is used in other places for
actually checking whether the state of the CPU is idle or not.

Hence split the use of that function based on the desired return value,
by introducing the available_idle_cpu() function.

This fixes a (slight) regression in that initial vCPU commit, because
some code paths (like the load-balancer) don't care and shouldn't care
if the vCPU is preempted or not, they just want to know if there's any
tasks on the CPU.
Signed-off-by: NRohit Jain <rohit.k.jain@oracle.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dhaval.giani@oracle.com
Cc: linux-kernel@vger.kernel.org
Cc: matt@codeblueprint.co.uk
Cc: steven.sistare@oracle.com
Cc: subhra.mazumdar@oracle.com
Link: http://lkml.kernel.org/r/1525883988-10356-1-git-send-email-rohit.k.jain@oracle.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      943d355d
    • M
      sched/numa: Stagger NUMA balancing scan periods for new threads · 13784475
      由 Mel Gorman 提交于 
      Threads share an address space and each can change the protections of the
same address space to trap NUMA faults. This is redundant and potentially
counter-productive as any thread doing the update will suffice. Potentially
only one thread is required but that thread may be idle or it may not have
any locality concerns and pick an unsuitable scan rate.

This patch uses independent scan period but they are staggered based on
the number of address space users when the thread is created.  The intent
is that threads will avoid scanning at the same time and have a chance
to adapt their scan rate later if necessary. This reduces the total scan
activity early in the lifetime of the threads.

The different in headline performance across a range of machines and
workloads is marginal but the system CPU usage is reduced as well as overall
scan activity.  The following is the time reported by NAS Parallel Benchmark
using unbound openmp threads and a D size class:

			      4.17.0-rc1             4.17.0-rc1
				 vanilla           stagger-v1r1
	Time bt.D      442.77 (   0.00%)      419.70 (   5.21%)
	Time cg.D      171.90 (   0.00%)      180.85 (  -5.21%)
	Time ep.D       33.10 (   0.00%)       32.90 (   0.60%)
	Time is.D        9.59 (   0.00%)        9.42 (   1.77%)
	Time lu.D      306.75 (   0.00%)      304.65 (   0.68%)
	Time mg.D       54.56 (   0.00%)       52.38 (   4.00%)
	Time sp.D     1020.03 (   0.00%)      903.77 (  11.40%)
	Time ua.D      400.58 (   0.00%)      386.49 (   3.52%)

Note it's not a universal win but we have no prior knowledge of which
thread matters but the number of threads created often exceeds the size
of the node when the threads are not bound. However, there is a reducation
of overall system CPU usage:

				    4.17.0-rc1             4.17.0-rc1
				       vanilla           stagger-v1r1
	sys-time-bt.D         48.78 (   0.00%)       48.22 (   1.15%)
	sys-time-cg.D         25.31 (   0.00%)       26.63 (  -5.22%)
	sys-time-ep.D          1.65 (   0.00%)        0.62 (  62.42%)
	sys-time-is.D         40.05 (   0.00%)       24.45 (  38.95%)
	sys-time-lu.D         37.55 (   0.00%)       29.02 (  22.72%)
	sys-time-mg.D         47.52 (   0.00%)       34.92 (  26.52%)
	sys-time-sp.D        119.01 (   0.00%)      109.05 (   8.37%)
	sys-time-ua.D         51.52 (   0.00%)       45.13 (  12.40%)

NUMA scan activity is also reduced:

	NUMA alloc local               1042828     1342670
	NUMA base PTE updates        140481138    93577468
	NUMA huge PMD updates           272171      180766
	NUMA page range updates      279832690   186129660
	NUMA hint faults               1395972     1193897
	NUMA hint local faults          877925      855053
	NUMA hint local percent             62          71
	NUMA pages migrated           12057909     9158023

Similar observations are made for other thread-intensive workloads. System
CPU usage is lower even though the headline gains in performance tend to be
small. For example, specjbb 2005 shows almost no difference in performance
but scan activity is reduced by a third on a 4-socket box. I didn't find
a workload (thread intensive or otherwise) that suffered badly.
Signed-off-by: NMel Gorman <mgorman@techsingularity.net>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20180504154109.mvrha2qo5wdl65vr@techsingularity.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      13784475
  7. 12 5月, 2018 1 次提交
    • M
      Revert "sched/numa: Delay retrying placement for automatic NUMA balance after wake_affine()" · 789ba280
      由 Mel Gorman 提交于 
      This reverts commit 7347fc87.

Srikar Dronamra pointed out that while the commit in question did show
a performance improvement on ppc64, it did so at the cost of disabling
active CPU migration by automatic NUMA balancing which was not the intent.
The issue was that a serious flaw in the logic failed to ever active balance
if SD_WAKE_AFFINE was disabled on scheduler domains. Even when it's enabled,
the logic is still bizarre and against the original intent.

Investigation showed that fixing the patch in either the way he suggested,
using the correct comparison for jiffies values or introducing a new
numa_migrate_deferred variable in task_struct all perform similarly to a
revert with a mix of gains and losses depending on the workload, machine
and socket count.

The original intent of the commit was to handle a problem whereby
wake_affine, idle balancing and automatic NUMA balancing disagree on the
appropriate placement for a task. This was particularly true for cases where
a single task was a massive waker of tasks but where wake_wide logic did
not apply.  This was particularly noticeable when a futex (a barrier) woke
all worker threads and tried pulling the wakees to the waker nodes. In that
specific case, it could be handled by tuning MPI or openMP appropriately,
but the behavior is not illogical and was worth attempting to fix. However,
the approach was wrong. Given that we're at rc4 and a fix is not obvious,
it's better to play safe, revert this commit and retry later.
Signed-off-by: NMel Gorman <mgorman@techsingularity.net>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: efault@gmx.de
Cc: ggherdovich@suse.cz
Cc: hpa@zytor.com
Cc: matt@codeblueprint.co.uk
Cc: mpe@ellerman.id.au
Link: http://lkml.kernel.org/r/20180509163115.6fnnyeg4vdm2ct4v@techsingularity.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      789ba280
  9. 09 5月, 2018 2 次提交
  11. 05 5月, 2018 2 次提交
  13. 04 5月, 2018 4 次提交
    • R
      sched/core: Don't schedule threads on pre-empted vCPUs · 247f2f6f
      由 Rohit Jain 提交于 
      In paravirt configurations today, spinlocks figure out whether a vCPU is
running to determine whether or not spinlock should bother spinning. We
can use the same logic to prioritize CPUs when scheduling threads. If a
vCPU has been pre-empted, it will incur the extra cost of VMENTER and
the time it actually spends to be running on the host CPU. If we had
other vCPUs which were actually running on the host CPU and idle we
should schedule threads there.

Performance numbers:

Note: With patch is referred to as Paravirt in the following and without
patch is referred to as Base.

1) When only 1 VM is running:

    a) Hackbench test on KVM 8 vCPUs, 10,000 loops (lower is better):

	+-------+-----------------+----------------+
	|Number |Paravirt         |Base            |
	|of     +---------+-------+-------+--------+
	|Threads|Average  |Std Dev|Average| Std Dev|
	+-------+---------+-------+-------+--------+
	|1      |1.817    |0.076  |1.721  | 0.067  |
	|2      |3.467    |0.120  |3.468  | 0.074  |
	|4      |6.266    |0.035  |6.314  | 0.068  |
	|8      |11.437   |0.105  |11.418 | 0.132  |
	|16     |21.862   |0.167  |22.161 | 0.129  |
	|25     |33.341   |0.326  |33.692 | 0.147  |
	+-------+---------+-------+-------+--------+

2) When two VMs are running with same CPU affinities:

    a) tbench test on VM 8 cpus

    Base:

	VM1:

	Throughput 220.59 MB/sec   1 clients  1 procs  max_latency=12.872 ms
	Throughput 448.716 MB/sec  2 clients  2 procs  max_latency=7.555 ms
	Throughput 861.009 MB/sec  4 clients  4 procs  max_latency=49.501 ms
	Throughput 1261.81 MB/sec  7 clients  7 procs  max_latency=76.990 ms

	VM2:

	Throughput 219.937 MB/sec  1 clients  1 procs  max_latency=12.517 ms
	Throughput 470.99 MB/sec   2 clients  2 procs  max_latency=12.419 ms
	Throughput 841.299 MB/sec  4 clients  4 procs  max_latency=37.043 ms
	Throughput 1240.78 MB/sec  7 clients  7 procs  max_latency=77.489 ms

    Paravirt:

	VM1:

	Throughput 222.572 MB/sec  1 clients  1 procs  max_latency=7.057 ms
	Throughput 485.993 MB/sec  2 clients  2 procs  max_latency=26.049 ms
	Throughput 947.095 MB/sec  4 clients  4 procs  max_latency=45.338 ms
	Throughput 1364.26 MB/sec  7 clients  7 procs  max_latency=145.124 ms

	VM2:

	Throughput 224.128 MB/sec  1 clients  1 procs  max_latency=4.564 ms
	Throughput 501.878 MB/sec  2 clients  2 procs  max_latency=11.061 ms
	Throughput 965.455 MB/sec  4 clients  4 procs  max_latency=45.370 ms
	Throughput 1359.08 MB/sec  7 clients  7 procs  max_latency=168.053 ms

    b) Hackbench with 4 fd 1,000,000 loops

	+-------+--------------------------------------+----------------------------------------+
	|Number |Paravirt                              |Base                                    |
	|of     +----------+--------+---------+--------+----------+--------+---------+----------+
	|Threads|Average1  |Std Dev1|Average2 | Std Dev|Average1  |Std Dev1|Average2 | Std Dev 2|
	+-------+----------+--------+---------+--------+----------+--------+---------+----------+
	|  1    | 3.748    | 0.620  | 3.576   | 0.432  | 4.006    | 0.395  | 3.446   | 0.787    |
	+-------+----------+--------+---------+--------+----------+--------+---------+----------+

    Note that this test was run just to show the interference effect
    over-subscription can have in baseline

    c) schbench results with 2 message groups on 8 vCPU VMs

	+-----------+-------+---------------+--------------+------------+
	|           |       | Paravirt      | Base         |            |
	+-----------+-------+-------+-------+-------+------+------------+
	|           |Threads| VM1   | VM2   |  VM1  | VM2  |%Improvement|
	+-----------+-------+-------+-------+-------+------+------------+
	|50.0000th  |    1  | 52    | 53    |  58   | 54   |  +6.25%    |
	|75.0000th  |    1  | 69    | 61    |  83   | 59   |  +8.45%    |
	|90.0000th  |    1  | 80    | 80    |  89   | 83   |  +6.98%    |
	|95.0000th  |    1  | 83    | 83    |  93   | 87   |  +7.78%    |
	|*99.0000th |    1  | 92    | 94    |  99   | 97   |  +5.10%    |
	|99.5000th  |    1  | 95    | 100   |  102  | 103  |  +4.88%    |
	|99.9000th  |    1  | 107   | 123   |  105  | 203  |  +25.32%   |
	+-----------+-------+-------+-------+-------+------+------------+
	|50.0000th  |    2  | 56    | 62    |  67   | 59   |  +6.35%    |
	|75.0000th  |    2  | 69    | 75    |  80   | 71   |  +4.64%    |
	|90.0000th  |    2  | 80    | 82    |  90   | 81   |  +5.26%    |
	|95.0000th  |    2  | 85    | 87    |  97   | 91   |  +8.51%    |
	|*99.0000th |    2  | 98    | 99    |  107  | 109  |  +8.79%    |
	|99.5000th  |    2  | 107   | 105   |  109  | 116  |  +5.78%    |
	|99.9000th  |    2  | 9968  | 609   |  875  | 3116 | -165.02%   |
	+-----------+-------+-------+-------+-------+------+------------+
	|50.0000th  |    4  | 78    | 77    |  78   | 79   |  +1.27%    |
	|75.0000th  |    4  | 98    | 106   |  100  | 104  |   0.00%    |
	|90.0000th  |    4  | 987   | 1001  |  995  | 1015 |  +1.09%    |
	|95.0000th  |    4  | 4136  | 5368  |  5752 | 5192 |  +13.16%   |
	|*99.0000th |    4  | 11632 | 11344 |  11024| 10736|  -5.59%    |
	|99.5000th  |    4  | 12624 | 13040 |  12720| 12144|  -3.22%    |
	|99.9000th  |    4  | 13168 | 18912 |  14992| 17824|  +2.24%    |
	+-----------+-------+-------+-------+-------+------+------------+

    Note: Improvement is measured for (VM1+VM2)
Signed-off-by: NRohit Jain <rohit.k.jain@oracle.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dhaval.giani@oracle.com
Cc: matt@codeblueprint.co.uk
Cc: steven.sistare@oracle.com
Cc: subhra.mazumdar@oracle.com
Link: http://lkml.kernel.org/r/1525294330-7759-1-git-send-email-rohit.k.jain@oracle.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      247f2f6f
    • V
      sched/fair: Avoid calling sync_entity_load_avg() unnecessarily · c976a862
      由 Viresh Kumar 提交于 
      Call sync_entity_load_avg() directly from find_idlest_cpu() instead of
select_task_rq_fair(), as that's where we need to use task's utilization
value. And call sync_entity_load_avg() only after making sure sched
domain spans over one of the allowed CPUs for the task.
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: http://lkml.kernel.org/r/cd019d1753824c81130eae7b43e2bbcec47cc1ad.1524738578.git.viresh.kumar@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>
      c976a862
    • V
      sched/fair: Rearrange select_task_rq_fair() to optimize it · f1d88b44
      由 Viresh Kumar 提交于 
      Rearrange select_task_rq_fair() a bit to avoid executing some
conditional statements in few specific code-paths. That gets rid of the
goto as well.

This shouldn't result in any functional changes.
Tested-by: NRohit Jain <rohit.k.jain@oracle.com>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NValentin Schneider <valentin.schneider@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: http://lkml.kernel.org/r/20831b8d237bf3a20e4e328286f678b425ff04c9.1524738578.git.viresh.kumar@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>
      f1d88b44
    • P
      sched/core: Introduce set_special_state() · b5bf9a90
      由 Peter Zijlstra 提交于 
      Gaurav reported a perceived problem with TASK_PARKED, which turned out
to be a broken wait-loop pattern in __kthread_parkme(), but the
reported issue can (and does) in fact happen for states that do not do
condition based sleeps.

When the 'current->state = TASK_RUNNING' store of a previous
(concurrent) try_to_wake_up() collides with the setting of a 'special'
sleep state, we can loose the sleep state.

Normal condition based wait-loops are immune to this problem, but for
sleep states that are not condition based are subject to this problem.

There already is a fix for TASK_DEAD. Abstract that and also apply it
to TASK_STOPPED and TASK_TRACED, both of which are also without
condition based wait-loop.
Reported-by: NGaurav Kohli <gkohli@codeaurora.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NOleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      b5bf9a90
  15. 03 5月, 2018 2 次提交
    • P
      kthread, sched/wait: Fix kthread_parkme() completion issue · 85f1abe0
      由 Peter Zijlstra 提交于 
      Even with the wait-loop fixed, there is a further issue with
kthread_parkme(). Upon hotplug, when we do takedown_cpu(),
smpboot_park_threads() can return before all those threads are in fact
blocked, due to the placement of the complete() in __kthread_parkme().

When that happens, sched_cpu_dying() -> migrate_tasks() can end up
migrating such a still runnable task onto another CPU.

Normally the task will have hit schedule() and gone to sleep by the
time we do kthread_unpark(), which will then do __kthread_bind() to
re-bind the task to the correct CPU.

However, when we loose the initial TASK_PARKED store to the concurrent
wakeup issue described previously, do the complete(), get migrated, it
is possible to either:

 - observe kthread_unpark()'s clearing of SHOULD_PARK and terminate
   the park and set TASK_RUNNING, or

 - __kthread_bind()'s wait_task_inactive() to observe the competing
   TASK_RUNNING store.

Either way the WARN() in __kthread_bind() will trigger and fail to
correctly set the CPU affinity.

Fix this by only issuing the complete() when the kthread has scheduled
out. This does away with all the icky 'still running' nonsense.

The alternative is to promote TASK_PARKED to a special state, this
guarantees wait_task_inactive() cannot observe a 'stale' TASK_RUNNING
and we'll end up doing the right thing, but this preserves the whole
icky business of potentially migating the still runnable thing.
Reported-by: NGaurav Kohli <gkohli@codeaurora.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      85f1abe0
    • V
      sched/fair: Fix the update of blocked load when newly idle · 457be908
      由 Vincent Guittot 提交于 
      With commit:

  31e77c93 ("sched/fair: Update blocked load when newly idle")

... we release the rq->lock when updating blocked load of idle CPUs.

This opens a time window during which another CPU can add a task to this
CPU's cfs_rq.

The check for newly added task of idle_balance() is not in the common path.
Move the out label to include this check.
Reported-by: NHeiner Kallweit <hkallweit1@gmail.com>
Tested-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 31e77c93 ("sched/fair: Update blocked load when newly idle")
Link: http://lkml.kernel.org/r/20180426103133.GA6953@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>
      457be908
  17. 09 4月, 2018 1 次提交
    • R
      sched: idle: Select idle state before stopping the tick · 554c8aa8
      由 Rafael J. Wysocki 提交于 
      In order to address the issue with short idle duration predictions
by the idle governor after the scheduler tick has been stopped,
reorder the code in cpuidle_idle_call() so that the governor idle
state selection runs before tick_nohz_idle_go_idle() and use the
"nohz" hint returned by cpuidle_select() to decide whether or not
to stop the tick.

This isn't straightforward, because menu_select() invokes
tick_nohz_get_sleep_length() to get the time to the next timer
event and the number returned by the latter comes from
__tick_nohz_idle_stop_tick().  Fortunately, however, it is possible
to compute that number without actually stopping the tick and with
the help of the existing code.

Namely, tick_nohz_get_sleep_length() can be made call
tick_nohz_next_event(), introduced earlier, to get the time to the
next non-highres timer event.  If that happens, tick_nohz_next_event()
need not be called by __tick_nohz_idle_stop_tick() again.

If it turns out that the scheduler tick cannot be stopped going
forward or the next timer event is too close for the tick to be
stopped, tick_nohz_get_sleep_length() can simply return the time to
the next event currently programmed into the corresponding clock
event device.

In addition to knowing the return value of tick_nohz_next_event(),
however, tick_nohz_get_sleep_length() needs to know the time to the
next highres timer event, but with the scheduler tick timer excluded,
which can be computed with the help of hrtimer_get_next_event().

That minimum of that number and the tick_nohz_next_event() return
value is the total time to the next timer event with the assumption
that the tick will be stopped.  It can be returned to the idle
governor which can use it for predicting idle duration (under the
assumption that the tick will be stopped) and deciding whether or
not it makes sense to stop the tick before putting the CPU into the
selected idle state.

With the above, the sleep_length field in struct tick_sched is not
necessary any more, so drop it.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=199227Reported-by: NDoug Smythies <dsmythies@telus.net>
Reported-by: NThomas Ilsche <thomas.ilsche@tu-dresden.de>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NFrederic Weisbecker <frederic@kernel.org>
      554c8aa8
  19. 06 4月, 2018 5 次提交
    • R
      cpuidle: Return nohz hint from cpuidle_select() · 45f1ff59
      由 Rafael J. Wysocki 提交于 
      Add a new pointer argument to cpuidle_select() and to the ->select
cpuidle governor callback to allow a boolean value indicating
whether or not the tick should be stopped before entering the
selected state to be returned from there.

Make the ladder governor ignore that pointer (to preserve its
current behavior) and make the menu governor return 'false" through
it if:
 (1) the idle exit latency is constrained at 0, or
 (2) the selected state is a polling one, or
 (3) the expected idle period duration is within the tick period
     range.

In addition to that, the correction factor computations in the menu
governor need to take the possibility that the tick may not be
stopped into account to avoid artificially small correction factor
values.  To that end, add a mechanism to record tick wakeups, as
suggested by Peter Zijlstra, and use it to modify the menu_update()
behavior when tick wakeup occurs.  Namely, if the CPU is woken up by
the tick and the return value of tick_nohz_get_sleep_length() is not
within the tick boundary, the predicted idle duration is likely too
short, so make menu_update() try to compensate for that by updating
the governor statistics as though the CPU was idle for a long time.

Since the value returned through the new argument pointer of
cpuidle_select() is not used by its caller yet, this change by
itself is not expected to alter the functionality of the code.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      45f1ff59
    • M
      kernel/fork.c: detect early free of a live mm · 3eda69c9
      由 Mark Rutland 提交于 
      KASAN splats indicate that in some cases we free a live mm, then
continue to access it, with potentially disastrous results.  This is
likely due to a mismatched mmdrop() somewhere in the kernel, but so far
the culprit remains elusive.

Let's have __mmdrop() verify that the mm isn't live for the current
task, similar to the existing check for init_mm.  This way, we can catch
this class of issue earlier, and without requiring KASAN.

Currently, idle_task_exit() leaves active_mm stale after it switches to
init_mm.  This isn't harmful, but will trigger the new assertions, so we
must adjust idle_task_exit() to update active_mm.

Link: http://lkml.kernel.org/r/20180312140103.19235-1-mark.rutland@arm.comSigned-off-by: NMark Rutland <mark.rutland@arm.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      3eda69c9
    • R
      sched: idle: Do not stop the tick before cpuidle_idle_call() · ed98c349
      由 Rafael J. Wysocki 提交于 
      Make cpuidle_idle_call() decide whether or not to stop the tick.

First, the cpuidle_enter_s2idle() path deals with the tick (and with
the entire timekeeping for that matter) by itself and it doesn't need
the tick to be stopped beforehand.

Second, to address the issue with short idle duration predictions
by the idle governor after the tick has been stopped, it will be
necessary to change the ordering of cpuidle_select() with respect
to tick_nohz_idle_stop_tick().  To prepare for that, put a
tick_nohz_idle_stop_tick() call in the same branch in which
cpuidle_select() is called.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: NFrederic Weisbecker <frederic@kernel.org>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      ed98c349
    • R
      sched: idle: Do not stop the tick upfront in the idle loop · 2aaf709a
      由 Rafael J. Wysocki 提交于 
      Push the decision whether or not to stop the tick somewhat deeper
into the idle loop.

Stopping the tick upfront leads to unpleasant outcomes in case the
idle governor doesn't agree with the nohz code on the duration of the
upcoming idle period.  Specifically, if the tick has been stopped and
the idle governor predicts short idle, the situation is bad regardless
of whether or not the prediction is accurate.  If it is accurate, the
tick has been stopped unnecessarily which means excessive overhead.
If it is not accurate, the CPU is likely to spend too much time in
the (shallow, because short idle has been predicted) idle state
selected by the governor [1].

As the first step towards addressing this problem, change the code
to make the tick stopping decision inside of the loop in do_idle().
In particular, do not stop the tick in the cpu_idle_poll() code path.
Also don't do that in tick_nohz_irq_exit() which doesn't really have
enough information on whether or not to stop the tick.

Link: https://marc.info/?l=linux-pm&m=150116085925208&w=2 # [1]
Link: https://tu-dresden.de/zih/forschung/ressourcen/dateien/projekte/haec/powernightmares.pdfSuggested-by: NFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: NFrederic Weisbecker <frederic@kernel.org>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      2aaf709a
    • R
      time: tick-sched: Reorganize idle tick management code · 0e776768
      由 Rafael J. Wysocki 提交于 
      Prepare the scheduler tick code for reworking the idle loop to
avoid stopping the tick in some cases.

The idea is to split the nohz idle entry call to decouple the idle
time stats accounting and preparatory work from the actual tick stop
code, in order to later be able to delay the tick stop once we reach
more power-knowledgeable callers.

Move away the tick_nohz_start_idle() invocation from
__tick_nohz_idle_enter(), rename the latter to
__tick_nohz_idle_stop_tick() and define tick_nohz_idle_stop_tick()
as a wrapper around it for calling it from the outside.

Make tick_nohz_idle_enter() only call tick_nohz_start_idle() instead
of calling the entire __tick_nohz_idle_enter(), add another wrapper
disabling and enabling interrupts around tick_nohz_idle_stop_tick()
and make the current callers of tick_nohz_idle_enter() call it too
to retain their current functionality.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: NFrederic Weisbecker <frederic@kernel.org>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      0e776768
  21. 05 4月, 2018 2 次提交
  23. 03 4月, 2018 1 次提交
  25. 01 4月, 2018 1 次提交
  27. 27 3月, 2018 1 次提交
  29. 24 3月, 2018 1 次提交
  31. 20 3月, 2018 9 次提交
    • J
      sched/debug: Adjust newlines for better alignment · e9ca2670
      由 Joe Lawrence 提交于 
      Scheduler debug stats include newlines that display out of alignment
when prefixed by timestamps.  For example, the dmesg utility:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  [   83.124251]
  runnable tasks:
   S           task   PID         tree-key  switches  prio     wait-time
  sum-exec        sum-sleep
  -----------------------------------------------------------------------------------------------------------

At the same time, some syslog utilities (like rsyslog by default) don't
like the additional newlines control characters, saving lines like this
to /var/log/messages:

  Mar 16 16:02:29 localhost kernel: #012runnable tasks:#12 S           task   PID         tree-key ...
                                    ^^^^               ^^^^
Clean these up by moving newline characters to their own SEQ_printf
invocation.  This leaves the /proc/sched_debug unchanged, but brings the
entire output into alignment when prefixed:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  [   62.410368] runnable tasks:
  [   62.410368]  S           task   PID         tree-key  switches  prio     wait-time             sum-exec        sum-sleep
  [   62.410369] -----------------------------------------------------------------------------------------------------------
  [   62.410369]  I  kworker/u12:0     5      1932.215593       332   120         0.000000         3.621252         0.000000 0 0 /

and no escaped control characters from rsyslog in /var/log/messages:

  Mar 16 16:15:06 localhost kernel: runnable tasks:
  Mar 16 16:15:06 localhost kernel: S           task   PID         tree-key  ...
Signed-off-by: NJoe Lawrence <joe.lawrence@redhat.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1521484555-8620-3-git-send-email-joe.lawrence@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      e9ca2670
    • J
      sched/debug: Fix per-task line continuation for console output · a8c024cd
      由 Joe Lawrence 提交于 
      When the SEQ_printf() macro prints to the console, it runs a simple
printk() without KERN_CONT "continued" line printing.  The result of
this is oddly wrapped task info, for example:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  runnable tasks:
  ...
  [   29.608611]  I
  [   29.608613]       rcu_sched     8      3252.013846      4087   120
  [   29.608614]         0.000000        29.090111         0.000000
  [   29.608615]  0 0
  [   29.608616]  /

Modify SEQ_printf to use pr_cont() for expected one-line results:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  runnable tasks:
  ...
  [  106.716329]  S        cpuhp/5    37      2006.315026        14   120         0.000000         0.496893         0.000000 0 0 /
Signed-off-by: NJoe Lawrence <joe.lawrence@redhat.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1521484555-8620-2-git-send-email-joe.lawrence@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      a8c024cd
    • P
      sched/wait: Improve __var_waitqueue() code generation · b3fc5c9b
      由 Peter Zijlstra 提交于 
      Since we fixed hash_64() to not suck there is no need to play games to
attempt to improve the hash value on 64-bit.

Also, since we don't use the bit value for the variables, use hash_ptr()
directly.

No change in functionality.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: George Spelvin <linux@sciencehorizons.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      b3fc5c9b
    • P
      sched/wait: Remove the wait_on_atomic_t() API · 9b8cce52
      由 Peter Zijlstra 提交于 
      There are no users left (everyone got converted to wait_var_event()), remove it.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      9b8cce52
    • P
      sched/wait: Introduce wait_var_event() · 6b2bb726
      由 Peter Zijlstra 提交于 
      As a replacement for the wait_on_atomic_t() API provide the
wait_var_event() API.

The wait_var_event() API is based on the very same hashed-waitqueue
idea, but doesn't care about the type (atomic_t) or the specific
condition (atomic_read() == 0). IOW. it's much more widely
applicable/flexible.

It shares all the benefits/disadvantages of a hashed-waitqueue
approach with the existing wait_on_atomic_t/wait_on_bit() APIs.

The API is modeled after the existing wait_event() API, but instead of
taking a wait_queue_head, it takes an address. This addresses is
hashed to obtain a wait_queue_head from the bit_wait_table.

Similar to the wait_event() API, it takes a condition expression as
second argument and will wait until this expression becomes true.

The following are (mostly) identical replacements:

	wait_on_atomic_t(&my_atomic, atomic_t_wait, TASK_UNINTERRUPTIBLE);
	wake_up_atomic_t(&my_atomic);

	wait_var_event(&my_atomic, !atomic_read(&my_atomic));
	wake_up_var(&my_atomic);

The only difference is that wake_up_var() is an unconditional wakeup
and doesn't check the previously hard-coded (atomic_read() == 0)
condition here. This is of little concequence, since most callers are
already conditional on atomic_dec_and_test() and the ones that are
not, are trivial to make so.
Tested-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>
      6b2bb726
    • P
      sched/fair: Update util_est only on util_avg updates · d519329f
      由 Patrick Bellasi 提交于 
      The estimated utilization of a task is currently updated every time the
task is dequeued. However, to keep overheads under control, PELT signals
are effectively updated at maximum once every 1ms.

Thus, for really short running tasks, it can happen that their util_avg
value has not been updates since their last enqueue.  If such tasks are
also frequently running tasks (e.g. the kind of workload generated by
hackbench) it can also happen that their util_avg is updated only every
few activations.

This means that updating util_est at every dequeue potentially introduces
not necessary overheads and it's also conceptually wrong if the util_avg
signal has never been updated during a task activation.

Let's introduce a throttling mechanism on task's util_est updates
to sync them with util_avg updates. To make the solution memory
efficient, both in terms of space and load/store operations, we encode a
synchronization flag into the LSB of util_est.enqueued.
This makes util_est an even values only metric, which is still
considered good enough for its purpose.
The synchronization bit is (re)set by __update_load_avg_se() once the
PELT signal of a task has been updated during its last activation.

Such a throttling mechanism allows to keep under control util_est
overheads in the wakeup hot path, thus making it a suitable mechanism
which can be enabled also on high-intensity workload systems.
Thus, this now switches on by default the estimation utilization
scheduler feature.
Suggested-by: NChris Redpath <chris.redpath@arm.com>
Signed-off-by: NPatrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Steve Muckle <smuckle@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Todd Kjos <tkjos@android.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Link: http://lkml.kernel.org/r/20180309095245.11071-5-patrick.bellasi@arm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      d519329f
    • P
      sched/cpufreq/schedutil: Use util_est for OPP selection · a07630b8
      由 Patrick Bellasi 提交于 
      When schedutil looks at the CPU utilization, the current PELT value for
that CPU is returned straight away. In certain scenarios this can have
undesired side effects and delays on frequency selection.

For example, since the task utilization is decayed at wakeup time, a
long sleeping big task newly enqueued does not add immediately a
significant contribution to the target CPU. This introduces some latency
before schedutil will be able to detect the best frequency required by
that task.

Moreover, the PELT signal build-up time is a function of the current
frequency, because of the scale invariant load tracking support. Thus,
starting from a lower frequency, the utilization build-up time will
increase even more and further delays the selection of the actual
frequency which better serves the task requirements.

In order to reduce these kind of latencies, we integrate the usage
of the CPU's estimated utilization in the sugov_get_util function.

This allows to properly consider the expected utilization of a CPU which,
for example, has just got a big task running after a long sleep period.
Ultimately this allows to select the best frequency to run a task
right after its wake-up.
Signed-off-by: NPatrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steve Muckle <smuckle@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Todd Kjos <tkjos@android.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: http://lkml.kernel.org/r/20180309095245.11071-4-patrick.bellasi@arm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      a07630b8
    • P
      sched/fair: Use util_est in LB and WU paths · f9be3e59
      由 Patrick Bellasi 提交于 
      When the scheduler looks at the CPU utilization, the current PELT value
for a CPU is returned straight away. In certain scenarios this can have
undesired side effects on task placement.

For example, since the task utilization is decayed at wakeup time, when
a long sleeping big task is enqueued it does not add immediately a
significant contribution to the target CPU.
As a result we generate a race condition where other tasks can be placed
on the same CPU while it is still considered relatively empty.

In order to reduce this kind of race conditions, this patch introduces the
required support to integrate the usage of the CPU's estimated utilization
in the wakeup path, via cpu_util_wake(), as well as in the load-balance
path, via cpu_util() which is used by update_sg_lb_stats().

The estimated utilization of a CPU is defined to be the maximum between
its PELT's utilization and the sum of the estimated utilization (at
previous dequeue time) of all the tasks currently RUNNABLE on that CPU.
This allows to properly represent the spare capacity of a CPU which, for
example, has just got a big task running since a long sleep period.
Signed-off-by: NPatrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Steve Muckle <smuckle@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Todd Kjos <tkjos@android.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Link: http://lkml.kernel.org/r/20180309095245.11071-3-patrick.bellasi@arm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      f9be3e59
    • P
      sched/fair: Add util_est on top of PELT · 7f65ea42
      由 Patrick Bellasi 提交于 
      The util_avg signal computed by PELT is too variable for some use-cases.
For example, a big task waking up after a long sleep period will have its
utilization almost completely decayed. This introduces some latency before
schedutil will be able to pick the best frequency to run a task.

The same issue can affect task placement. Indeed, since the task
utilization is already decayed at wakeup, when the task is enqueued in a
CPU, this can result in a CPU running a big task as being temporarily
represented as being almost empty. This leads to a race condition where
other tasks can be potentially allocated on a CPU which just started to run
a big task which slept for a relatively long period.

Moreover, the PELT utilization of a task can be updated every [ms], thus
making it a continuously changing value for certain longer running
tasks. This means that the instantaneous PELT utilization of a RUNNING
task is not really meaningful to properly support scheduler decisions.

For all these reasons, a more stable signal can do a better job of
representing the expected/estimated utilization of a task/cfs_rq.
Such a signal can be easily created on top of PELT by still using it as
an estimator which produces values to be aggregated on meaningful
events.

This patch adds a simple implementation of util_est, a new signal built on
top of PELT's util_avg where:

    util_est(task) = max(task::util_avg, f(task::util_avg@dequeue))

This allows to remember how big a task has been reported by PELT in its
previous activations via f(task::util_avg@dequeue), which is the new
_task_util_est(struct task_struct*) function added by this patch.

If a task should change its behavior and it runs longer in a new
activation, after a certain time its util_est will just track the
original PELT signal (i.e. task::util_avg).

The estimated utilization of cfs_rq is defined only for root ones.
That's because the only sensible consumer of this signal are the
scheduler and schedutil when looking for the overall CPU utilization
due to FAIR tasks.

For this reason, the estimated utilization of a root cfs_rq is simply
defined as:

    util_est(cfs_rq) = max(cfs_rq::util_avg, cfs_rq::util_est::enqueued)

where:

    cfs_rq::util_est::enqueued = sum(_task_util_est(task))
                                 for each RUNNABLE task on that root cfs_rq

It's worth noting that the estimated utilization is tracked only for
objects of interests, specifically:

 - Tasks: to better support tasks placement decisions
 - root cfs_rqs: to better support both tasks placement decisions as
                 well as frequencies selection
Signed-off-by: NPatrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Steve Muckle <smuckle@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Todd Kjos <tkjos@android.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Link: http://lkml.kernel.org/r/20180309095245.11071-2-patrick.bellasi@arm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      7f65ea42
  33. 09 3月, 2018 1 次提交