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  1. 17 12月, 2013 1 次提交
  3. 11 12月, 2013 1 次提交
    • P
      sched/fair: Rework sched_fair time accounting · 9dbdb155
      由 Peter Zijlstra 提交于 
      Christian suffers from a bad BIOS that wrecks his i5's TSC sync. This
results in him occasionally seeing time going backwards - which
crashes the scheduler ...

Most of our time accounting can actually handle that except the most
common one; the tick time update of sched_fair.

There is a further problem with that code; previously we assumed that
because we get a tick every TICK_NSEC our time delta could never
exceed 32bits and math was simpler.

However, ever since Frederic managed to get NO_HZ_FULL merged; this is
no longer the case since now a task can run for a long time indeed
without getting a tick. It only takes about ~4.2 seconds to overflow
our u32 in nanoseconds.

This means we not only need to better deal with time going backwards;
but also means we need to be able to deal with large deltas.

This patch reworks the entire code and uses mul_u64_u32_shr() as
proposed by Andy a long while ago.

We express our virtual time scale factor in a u32 multiplier and shift
right and the 32bit mul_u64_u32_shr() implementation reduces to a
single 32x32->64 multiply if the time delta is still short (common
case).

For 64bit a 64x64->128 multiply can be used if ARCH_SUPPORTS_INT128.
Reported-and-Tested-by: NChristian Engelmayer <cengelma@gmx.at>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: fweisbec@gmail.com
Cc: Paul Turner <pjt@google.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20131118172706.GI3866@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      9dbdb155
  5. 05 12月, 2013 1 次提交
  7. 27 11月, 2013 2 次提交
  9. 20 11月, 2013 1 次提交
  11. 13 11月, 2013 3 次提交
  13. 06 11月, 2013 2 次提交
    • P
      sched: Remove unnecessary iteration over sched domains to update nr_busy_cpus · 37dc6b50
      由 Preeti U Murthy 提交于 
      nr_busy_cpus parameter is used by nohz_kick_needed() to find out the
number of busy cpus in a sched domain which has SD_SHARE_PKG_RESOURCES
flag set.  Therefore instead of updating nr_busy_cpus at every level
of sched domain, since it is irrelevant, we can update this parameter
only at the parent domain of the sd which has this flag set. Introduce
a per-cpu parameter sd_busy which represents this parent domain.

In nohz_kick_needed() we directly query the nr_busy_cpus parameter
associated with the groups of sd_busy.

By associating sd_busy with the highest domain which has
SD_SHARE_PKG_RESOURCES flag set, we cover all lower level domains
which could have this flag set and trigger nohz_idle_balancing if any
of the levels have more than one busy cpu.

sd_busy is irrelevant for asymmetric load balancing. However sd_asym
has been introduced to represent the highest sched domain which has
SD_ASYM_PACKING flag set so that it can be queried directly when
required.

While we are at it, we might as well change the nohz_idle parameter to
be updated at the sd_busy domain level alone and not the base domain
level of a CPU.  This will unify the concept of busy cpus at just one
level of sched domain where it is currently used.

Signed-off-by: Preeti U Murthy<preeti@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: svaidy@linux.vnet.ibm.com
Cc: vincent.guittot@linaro.org
Cc: bitbucket@online.de
Cc: benh@kernel.crashing.org
Cc: anton@samba.org
Cc: Morten.Rasmussen@arm.com
Cc: pjt@google.com
Cc: peterz@infradead.org
Cc: mikey@neuling.org
Link: http://lkml.kernel.org/r/20131030031252.23426.4417.stgit@preeti.in.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      37dc6b50
    • V
      sched: Fix asymmetric scheduling for POWER7 · 2042abe7
      由 Vaidyanathan Srinivasan 提交于 
      Asymmetric scheduling within a core is a scheduler loadbalancing
feature that is triggered when SD_ASYM_PACKING flag is set.  The goal
for the load balancer is to move tasks to lower order idle SMT threads
within a core on a POWER7 system.

In nohz_kick_needed(), we intend to check if our sched domain (core)
is completely busy or we have idle cpu.

The following check for SD_ASYM_PACKING:

    (cpumask_first_and(nohz.idle_cpus_mask, sched_domain_span(sd)) < cpu)

already covers the case of checking if the domain has an idle cpu,
because cpumask_first_and() will not yield any set bits if this domain
has no idle cpu.

Hence, nr_busy check against group weight can be removed.
Reported-by: NMichael Neuling <michael.neuling@au1.ibm.com>
Signed-off-by: NVaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Tested-by: NMichael Neuling <mikey@neuling.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: vincent.guittot@linaro.org
Cc: bitbucket@online.de
Cc: benh@kernel.crashing.org
Cc: anton@samba.org
Cc: Morten.Rasmussen@arm.com
Cc: pjt@google.com
Link: http://lkml.kernel.org/r/20131030031242.23426.13019.stgit@preeti.in.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      2042abe7
  15. 29 10月, 2013 5 次提交
  17. 16 10月, 2013 1 次提交
    • P
      sched: Fix race in migrate_swap_stop() · 74602315
      由 Peter Zijlstra 提交于 
      There is a subtle race in migrate_swap, when task P, on CPU A, decides to swap
places with task T, on CPU B.

Task P:
  - call migrate_swap
Task T:
  - go to sleep, removing itself from the runqueue
Task P:
  - double lock the runqueues on CPU A & B
Task T:
  - get woken up, place itself on the runqueue of CPU C
Task P:
  - see that task T is on a runqueue, and pretend to remove it
    from the runqueue on CPU B

Now CPUs B & C both have corrupted scheduler data structures.

This patch fixes it, by holding the pi_lock for both of the tasks
involved in the migrate swap. This prevents task T from waking up,
and placing itself onto another runqueue, until after migrate_swap
has released all locks.

This means that, when migrate_swap checks, task T will be either
on the runqueue where it was originally seen, or not on any
runqueue at all. Migrate_swap deals correctly with of those cases.
Tested-by: NJoe Mario <jmario@redhat.com>
Acked-by: NMel Gorman <mgorman@suse.de>
Reviewed-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: hannes@cmpxchg.org
Cc: aarcange@redhat.com
Cc: srikar@linux.vnet.ibm.com
Cc: tglx@linutronix.de
Cc: hpa@zytor.com
Link: http://lkml.kernel.org/r/20131010181722.GO13848@laptop.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      74602315
  19. 14 10月, 2013 1 次提交
  21. 13 10月, 2013 1 次提交
  23. 09 10月, 2013 21 次提交