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  1. 01 2月, 2009 1 次提交
  3. 04 1月, 2009 1 次提交
    • M
      sched: put back some stack hog changes that were undone in kernel/sched.c · 6ca09dfc
      由 Mike Travis 提交于 
      Impact: prevents panic from stack overflow on numa-capable machines.

Some of the "removal of stack hogs" changes in kernel/sched.c by using
node_to_cpumask_ptr were undone by the early cpumask API updates, and
causes a panic due to stack overflow.  This patch undoes those changes
by using cpumask_of_node() which returns a 'const struct cpumask *'.

In addition, cpu_coregoup_map is replaced with cpu_coregroup_mask further
reducing stack usage.  (Both of these updates removed 9 FIXME's!)

Also:
   Pick up some remaining changes from the old 'cpumask_t' functions to
   the new 'struct cpumask *' functions.

   Optimize memory traffic by allocating each percpu local_cpu_mask on the
   same node as the referring cpu.
Signed-off-by: NMike Travis <travis@sgi.com>
Acked-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      6ca09dfc
  5. 17 12月, 2008 1 次提交
  7. 29 11月, 2008 1 次提交
    • A
      sched: move double_unlock_balance() higher · 70574a99
      由 Alexey Dobriyan 提交于 
      Move double_lock_balance()/double_unlock_balance() higher to fix the following
with gcc-3.4.6:

   CC      kernel/sched.o
 In file included from kernel/sched.c:1605:
 kernel/sched_rt.c: In function `find_lock_lowest_rq':
 kernel/sched_rt.c:914: sorry, unimplemented: inlining failed in call to 'double_unlock_balance': function body not available
 kernel/sched_rt.c:1077: sorry, unimplemented: called from here
 make[2]: *** [kernel/sched.o] Error 1
Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      70574a99
  9. 26 11月, 2008 1 次提交
  11. 25 11月, 2008 5 次提交
  13. 07 11月, 2008 1 次提交
    • S
      sched, lockdep: inline double_unlock_balance() · cf7f8690
      由 Sripathi Kodi 提交于 
      We have a test case which measures the variation in the amount of time
needed to perform a fixed amount of work on the preempt_rt kernel. We
started seeing deterioration in it's performance recently. The test
should never take more than 10 microseconds, but we started 5-10%
failure rate.

Using elimination method, we traced the problem to commit
1b12bbc7 (lockdep: re-annotate
scheduler runqueues).

When LOCKDEP is disabled, this patch only adds an additional function
call to double_unlock_balance(). Hence I inlined double_unlock_balance()
and the problem went away. Here is a patch to make this change.
Signed-off-by: NSripathi Kodi <sripathik@in.ibm.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      cf7f8690
  15. 03 11月, 2008 1 次提交
    • D
      sched/rt: small optimization to update_curr_rt() · e113a745
      由 Dimitri Sivanich 提交于 
      Impact: micro-optimization to SCHED_FIFO/RR scheduling

A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
before taking the rt_runtime_lock?

Peter Zijlstra observes:

> Yes, I think its ok to do so.
>
> Like pointed out in the other thread, there are two races:
>
>  - sched_rt_runtime() going to RUNTIME_INF, and that will be handled
>    properly by sched_rt_runtime_exceeded()
>
>  - sched_rt_runtime() going to !RUNTIME_INF, and here we can miss an
>    accounting cycle, but I don't think that is something to worry too
>    much about.
Signed-off-by: NDimitri Sivanich <sivanich@sgi.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

--

 kernel/sched_rt.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
      e113a745
  17. 22 10月, 2008 1 次提交
  19. 04 10月, 2008 1 次提交
    • D
      sched_rt.c: resch needed in rt_rq_enqueue() for the root rt_rq · f6121f4f
      由 Dario Faggioli 提交于 
      While working on the new version of the code for SCHED_SPORADIC I
noticed something strange in the present throttling mechanism. More
specifically in the throttling timer handler in sched_rt.c
(do_sched_rt_period_timer()) and in rt_rq_enqueue().

The problem is that, when unthrottling a runqueue, rt_rq_enqueue() only
asks for rescheduling if the runqueue has a sched_entity associated to
it (i.e., rt_rq->rt_se != NULL).
Now, if the runqueue is the root rq (which has a rt_se = NULL)
rescheduling does not take place, and it is delayed to some undefined
instant in the future.

This imply some random bandwidth usage by the RT tasks under throttling.
For instance, setting rt_runtime_us/rt_period_us = 950ms/1000ms an RT
task will get less than 95%. In our tests we got something varying
between 70% to 95%.
Using smaller time values, e.g., 95ms/100ms, things are even worse, and
I can see values also going down to 20-25%!!

The tests we performed are simply running 'yes' as a SCHED_FIFO task,
and checking the CPU usage with top, but we can investigate thoroughly
if you think it is needed.

Things go much better, for us, with the attached patch... Don't know if
it is the best approach, but it solved the issue for us.
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NMichael Trimarchi <trimarchimichael@yahoo.it>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      f6121f4f
  21. 23 9月, 2008 1 次提交
  23. 22 9月, 2008 1 次提交
  25. 14 9月, 2008 1 次提交
    • F
      timers: fix itimer/many thread hang · f06febc9
      由 Frank Mayhar 提交于 
      Overview

This patch reworks the handling of POSIX CPU timers, including the
ITIMER_PROF, ITIMER_VIRT timers and rlimit handling.  It was put together
with the help of Roland McGrath, the owner and original writer of this code.

The problem we ran into, and the reason for this rework, has to do with using
a profiling timer in a process with a large number of threads.  It appears
that the performance of the old implementation of run_posix_cpu_timers() was
at least O(n*3) (where "n" is the number of threads in a process) or worse.
Everything is fine with an increasing number of threads until the time taken
for that routine to run becomes the same as or greater than the tick time, at
which point things degrade rather quickly.

This patch fixes bug 9906, "Weird hang with NPTL and SIGPROF."

Code Changes

This rework corrects the implementation of run_posix_cpu_timers() to make it
run in constant time for a particular machine.  (Performance may vary between
one machine and another depending upon whether the kernel is built as single-
or multiprocessor and, in the latter case, depending upon the number of
running processors.)  To do this, at each tick we now update fields in
signal_struct as well as task_struct.  The run_posix_cpu_timers() function
uses those fields to make its decisions.

We define a new structure, "task_cputime," to contain user, system and
scheduler times and use these in appropriate places:

struct task_cputime {
	cputime_t utime;
	cputime_t stime;
	unsigned long long sum_exec_runtime;
};

This is included in the structure "thread_group_cputime," which is a new
substructure of signal_struct and which varies for uniprocessor versus
multiprocessor kernels.  For uniprocessor kernels, it uses "task_cputime" as
a simple substructure, while for multiprocessor kernels it is a pointer:

struct thread_group_cputime {
	struct task_cputime totals;
};

struct thread_group_cputime {
	struct task_cputime *totals;
};

We also add a new task_cputime substructure directly to signal_struct, to
cache the earliest expiration of process-wide timers, and task_cputime also
replaces the it_*_expires fields of task_struct (used for earliest expiration
of thread timers).  The "thread_group_cputime" structure contains process-wide
timers that are updated via account_user_time() and friends.  In the non-SMP
case the structure is a simple aggregator; unfortunately in the SMP case that
simplicity was not achievable due to cache-line contention between CPUs (in
one measured case performance was actually _worse_ on a 16-cpu system than
the same test on a 4-cpu system, due to this contention).  For SMP, the
thread_group_cputime counters are maintained as a per-cpu structure allocated
using alloc_percpu().  The timer functions update only the timer field in
the structure corresponding to the running CPU, obtained using per_cpu_ptr().

We define a set of inline functions in sched.h that we use to maintain the
thread_group_cputime structure and hide the differences between UP and SMP
implementations from the rest of the kernel.  The thread_group_cputime_init()
function initializes the thread_group_cputime structure for the given task.
The thread_group_cputime_alloc() is a no-op for UP; for SMP it calls the
out-of-line function thread_group_cputime_alloc_smp() to allocate and fill
in the per-cpu structures and fields.  The thread_group_cputime_free()
function, also a no-op for UP, in SMP frees the per-cpu structures.  The
thread_group_cputime_clone_thread() function (also a UP no-op) for SMP calls
thread_group_cputime_alloc() if the per-cpu structures haven't yet been
allocated.  The thread_group_cputime() function fills the task_cputime
structure it is passed with the contents of the thread_group_cputime fields;
in UP it's that simple but in SMP it must also safely check that tsk->signal
is non-NULL (if it is it just uses the appropriate fields of task_struct) and,
if so, sums the per-cpu values for each online CPU.  Finally, the three
functions account_group_user_time(), account_group_system_time() and
account_group_exec_runtime() are used by timer functions to update the
respective fields of the thread_group_cputime structure.

Non-SMP operation is trivial and will not be mentioned further.

The per-cpu structure is always allocated when a task creates its first new
thread, via a call to thread_group_cputime_clone_thread() from copy_signal().
It is freed at process exit via a call to thread_group_cputime_free() from
cleanup_signal().

All functions that formerly summed utime/stime/sum_sched_runtime values from
from all threads in the thread group now use thread_group_cputime() to
snapshot the values in the thread_group_cputime structure or the values in
the task structure itself if the per-cpu structure hasn't been allocated.

Finally, the code in kernel/posix-cpu-timers.c has changed quite a bit.
The run_posix_cpu_timers() function has been split into a fast path and a
slow path; the former safely checks whether there are any expired thread
timers and, if not, just returns, while the slow path does the heavy lifting.
With the dedicated thread group fields, timers are no longer "rebalanced" and
the process_timer_rebalance() function and related code has gone away.  All
summing loops are gone and all code that used them now uses the
thread_group_cputime() inline.  When process-wide timers are set, the new
task_cputime structure in signal_struct is used to cache the earliest
expiration; this is checked in the fast path.

Performance

The fix appears not to add significant overhead to existing operations.  It
generally performs the same as the current code except in two cases, one in
which it performs slightly worse (Case 5 below) and one in which it performs
very significantly better (Case 2 below).  Overall it's a wash except in those
two cases.

I've since done somewhat more involved testing on a dual-core Opteron system.

Case 1: With no itimer running, for a test with 100,000 threads, the fixed
	kernel took 1428.5 seconds, 513 seconds more than the unfixed system,
	all of which was spent in the system.  There were twice as many
	voluntary context switches with the fix as without it.

Case 2: With an itimer running at .01 second ticks and 4000 threads (the most
	an unmodified kernel can handle), the fixed kernel ran the test in
	eight percent of the time (5.8 seconds as opposed to 70 seconds) and
	had better tick accuracy (.012 seconds per tick as opposed to .023
	seconds per tick).

Case 3: A 4000-thread test with an initial timer tick of .01 second and an
	interval of 10,000 seconds (i.e. a timer that ticks only once) had
	very nearly the same performance in both cases:  6.3 seconds elapsed
	for the fixed kernel versus 5.5 seconds for the unfixed kernel.

With fewer threads (eight in these tests), the Case 1 test ran in essentially
the same time on both the modified and unmodified kernels (5.2 seconds versus
5.8 seconds).  The Case 2 test ran in about the same time as well, 5.9 seconds
versus 5.4 seconds but again with much better tick accuracy, .013 seconds per
tick versus .025 seconds per tick for the unmodified kernel.

Since the fix affected the rlimit code, I also tested soft and hard CPU limits.

Case 4: With a hard CPU limit of 20 seconds and eight threads (and an itimer
	running), the modified kernel was very slightly favored in that while
	it killed the process in 19.997 seconds of CPU time (5.002 seconds of
	wall time), only .003 seconds of that was system time, the rest was
	user time.  The unmodified kernel killed the process in 20.001 seconds
	of CPU (5.014 seconds of wall time) of which .016 seconds was system
	time.  Really, though, the results were too close to call.  The results
	were essentially the same with no itimer running.

Case 5: With a soft limit of 20 seconds and a hard limit of 2000 seconds
	(where the hard limit would never be reached) and an itimer running,
	the modified kernel exhibited worse tick accuracy than the unmodified
	kernel: .050 seconds/tick versus .028 seconds/tick.  Otherwise,
	performance was almost indistinguishable.  With no itimer running this
	test exhibited virtually identical behavior and times in both cases.

In times past I did some limited performance testing.  those results are below.

On a four-cpu Opteron system without this fix, a sixteen-thread test executed
in 3569.991 seconds, of which user was 3568.435s and system was 1.556s.  On
the same system with the fix, user and elapsed time were about the same, but
system time dropped to 0.007 seconds.  Performance with eight, four and one
thread were comparable.  Interestingly, the timer ticks with the fix seemed
more accurate:  The sixteen-thread test with the fix received 149543 ticks
for 0.024 seconds per tick, while the same test without the fix received 58720
for 0.061 seconds per tick.  Both cases were configured for an interval of
0.01 seconds.  Again, the other tests were comparable.  Each thread in this
test computed the primes up to 25,000,000.

I also did a test with a large number of threads, 100,000 threads, which is
impossible without the fix.  In this case each thread computed the primes only
up to 10,000 (to make the runtime manageable).  System time dominated, at
1546.968 seconds out of a total 2176.906 seconds (giving a user time of
629.938s).  It received 147651 ticks for 0.015 seconds per tick, still quite
accurate.  There is obviously no comparable test without the fix.
Signed-off-by: NFrank Mayhar <fmayhar@google.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      f06febc9
  27. 11 9月, 2008 1 次提交
    • Z
      sched: fix 2.6.27-rc5 couldn't boot on tulsa machine randomly · baf25731
      由 Zhang, Yanmin 提交于 
      On my tulsa x86-64 machine, kernel 2.6.25-rc5 couldn't boot randomly.

Basically, function __enable_runtime forgets to reset rt_rq->rt_throttled
to 0. When every cpu is up, per-cpu migration_thread is created and it runs
very fast, sometimes to mark the corresponding rt_rq->rt_throttled to 1 very
quickly. After all cpus are up, with below calling chain:

   sched_init_smp => arch_init_sched_domains => build_sched_domains => ...
=> cpu_attach_domain => rq_attach_root => set_rq_online => ...
=> _enable_runtime

_enable_runtime is called against every rt_rq again, so rt_rq->rt_time is
reset to 0, but rt_rq->rt_throttled might be still 1. Later on function
do_sched_rt_period_timer couldn't reset it, and all RT tasks couldn't be
scheduled to run on that cpu. here is RT task migration_thread which is
woken up when a task is migrated to another cpu.

Below patch fixes it against 2.6.27-rc5.
Signed-off-by: NZhang Yanmin <yanmin_zhang@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      baf25731
  29. 28 8月, 2008 2 次提交
    • P
      sched: rt-bandwidth accounting fix · cc2991cf
      由 Peter Zijlstra 提交于 
      It fixes an accounting bug where we would continue accumulating runtime
even though the bandwidth control is disabled. This would lead to very long
throttle periods once bandwidth control gets turned on again.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      cc2991cf
    • J
      sched: fix sched_rt_rq_enqueue() resched idle · f3ade837
      由 John Blackwood 提交于 
      When sysctl_sched_rt_runtime is set to something other than -1 and the
CONFIG_RT_GROUP_SCHED kernel parameter is NOT enabled, we get into a state
where we see one or more CPUs idling forvever even though there are
real-time
tasks in their rt runqueue that are able to run (no longer throttled).

The sequence is:

- A real-time task is running when the timer sets the rt runqueue
    to throttled, and the rt task is resched_task()ed and switched
    out, and idle is switched in since there are no non-rt tasks to
    run on that cpu.

- Eventually the do_sched_rt_period_timer() runs and un-throttles
    the rt runqueue, but we just exit the timer interrupt and go back
    to executing the idle task in the idle loop forever.

If we change the sched_rt_rq_enqueue() routine to use some of the code
from the CONFIG_RT_GROUP_SCHED enabled version of this same routine and
resched_task() the currently executing task (idle in our case) if it is
a lower priority task than the higher rt task in the now un-throttled
runqueue, the problem is no longer observed.
Signed-off-by: NJohn Blackwood <john.blackwood@ccur.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      f3ade837
  31. 19 8月, 2008 2 次提交
  33. 14 8月, 2008 1 次提交
  35. 11 8月, 2008 1 次提交
    • P
      lockdep: re-annotate scheduler runqueues · 1b12bbc7
      由 Peter Zijlstra 提交于 
      Instead of using a per-rq lock class, use the regular nesting operations.

However, take extra care with double_lock_balance() as it can release the
already held rq->lock (and therefore change its nesting class).

So what can happen is:

 spin_lock(rq->lock);	// this rq subclass 0

 double_lock_balance(rq, other_rq);
   // release rq
   // acquire other_rq->lock subclass 0
   // acquire rq->lock subclass 1

 spin_unlock(other_rq->lock);

leaving you with rq->lock in subclass 1

So a subsequent double_lock_balance() call can try to nest a subclass 1
lock while already holding a subclass 1 lock.

Fix this by introducing double_unlock_balance() which releases the other
rq's lock, but also re-sets the subclass for this rq's lock to 0.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      1b12bbc7
  37. 24 7月, 2008 1 次提交
  39. 18 7月, 2008 3 次提交
  41. 27 6月, 2008 3 次提交
  43. 20 6月, 2008 5 次提交
  45. 19 6月, 2008 2 次提交
  47. 18 6月, 2008 1 次提交
    • D
      sched: rework of "prioritize non-migratable tasks over migratable ones" · 20b6331b
      由 Dmitry Adamushko 提交于 
      regarding this commit: 45c01e82

I think we can do it simpler. Please take a look at the patch below.

Instead of having 2 separate arrays (which is + ~800 bytes on x86_32 and
twice so on x86_64), let's add "exclusive" (the ones that are bound to
this CPU) tasks to the head of the queue and "shared" ones -- to the
end.

In case of a few newly woken up "exclusive" tasks, they are 'stacked'
(not queued as now), meaning that a task {i+1} is being placed in front
of the previously woken up task {i}. But I don't think that this
behavior may cause any realistic problems.

There are a couple of changes on top of this one.

(1) in check_preempt_curr_rt()

I don't think there is a need for the "pick_next_rt_entity(rq, &rq->rt)
!= &rq->curr->rt" check.

enqueue_task_rt(p) and check_preempt_curr_rt() are always called one
after another with rq->lock being held so the following check
"p->rt.nr_cpus_allowed == 1 && rq->curr->rt.nr_cpus_allowed != 1" should
be enough (well, just its left part) to guarantee that 'p' has been
queued in front of the 'curr'.

(2) in set_cpus_allowed_rt()

I don't thinks there is a need for requeue_task_rt() here.

Perhaps, the only case when 'requeue' (+ reschedule) might be useful is
as follows:

i) weight == 1 && cpu_isset(task_cpu(p), *new_mask)

i.e. a task is being bound to this CPU);

ii) 'p' != rq->curr

but here, 'p' has already been on this CPU for a while and was not
migrated. i.e. it's possible that 'rq->curr' would not have high chances
to be migrated right at this particular moment (although, has chance in
a bit longer term), should we allow it to be preempted.

Anyway, I think we should not perhaps make it more complex trying to
address some rare corner cases. For instance, that's why a single queue
approach would be preferable. Unless I'm missing something obvious, this
approach gives us similar functionality at lower cost.

Verified only compilation-wise.

(Almost)-Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      20b6331b
  49. 10 6月, 2008 1 次提交
    • P
      sched: fix hotplug cpus on ia64 · 7def2be1
      由 Peter Zijlstra 提交于 
      Cliff Wickman wrote:

> I built an ia64 kernel from Andrew's tree (2.6.26-rc2-mm1)
> and get a very predictable hotplug cpu problem.
> billberry1:/tmp/cpw # ./dis
> disabled cpu 17
> enabled cpu 17
> billberry1:/tmp/cpw # ./dis
> disabled cpu 17
> enabled cpu 17
> billberry1:/tmp/cpw # ./dis
>
> The script that disables the cpu always hangs (unkillable)
> on the 3rd attempt.
>
> And a bit further:
> The kstopmachine thread always sits on the run queue (real time) for about
> 30 minutes before running.

this fix solves some (but not all) issues between CPU hotplug and
RT bandwidth throttling.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      7def2be1