Commit Graph

450 Commits

Author SHA1 Message Date
Ken Chen
b30aef17f7 sched: Fix erroneous all_pinned logic
The scheduler load balancer has specific code to deal with cases of
unbalanced system due to lots of unmovable tasks (for example because of
hard CPU affinity). In those situation, it excludes the busiest CPU that
has pinned tasks for load balance consideration such that it can perform
second 2nd load balance pass on the rest of the system.

This all works as designed if there is only one cgroup in the system.

However, when we have multiple cgroups, this logic has false positives and
triggers multiple load balance passes despite there are actually no pinned
tasks at all.

The reason it has false positives is that the all pinned logic is deep in
the lowest function of can_migrate_task() and is too low level:

load_balance_fair() iterates each task group and calls balance_tasks() to
migrate target load. Along the way, balance_tasks() will also set a
all_pinned variable. Given that task-groups are iterated, this all_pinned
variable is essentially the status of last group in the scanning process.
Task group can have number of reasons that no load being migrated, none
due to cpu affinity. However, this status bit is being propagated back up
to the higher level load_balance(), which incorrectly think that no tasks
were moved.  It kick off the all pinned logic and start multiple passes
attempt to move load onto puller CPU.

To fix this, move the all_pinned aggregation up at the iterator level.
This ensures that the status is aggregated over all task-groups, not just
last one in the list.

Signed-off-by: Ken Chen <kenchen@google.com>
Cc: stable@kernel.org
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/BANLkTi=ernzNawaR5tJZEsV_QVnfxqXmsQ@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-04-11 11:08:54 +02:00
Ken Chen
b0432d8f16 sched: Fix sched-domain avg_load calculation
In function find_busiest_group(), the sched-domain avg_load isn't
calculated at all if there is a group imbalance within the domain. This
will cause erroneous imbalance calculation.

The reason is that calculate_imbalance() sees sds->avg_load = 0 and it
will dump entire sds->max_load into imbalance variable, which is used
later on to migrate entire load from busiest CPU to the puller CPU.

This has two really bad effect:

1. stampede of task migration, and they won't be able to break out
   of the bad state because of positive feedback loop: large load
   delta -> heavier load migration -> larger imbalance and the cycle
   goes on.

2. severe imbalance in CPU queue depth.  This causes really long
   scheduling latency blip which affects badly on application that
   has tight latency requirement.

The fix is to have kernel calculate domain avg_load in both cases. This
will ensure that imbalance calculation is always sensible and the target
is usually half way between busiest and puller CPU.

Signed-off-by: Ken Chen <kenchen@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/20110408002322.3A0D812217F@elm.corp.google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-04-11 11:08:54 +02:00
Linus Torvalds
8b9686ff4d Merge branches 'x86-fixes-for-linus', 'sched-fixes-for-linus', 'timers-fixes-for-linus', 'irq-fixes-for-linus' and 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86-32, fpu: Fix FPU exception handling on non-SSE systems
  x86, hibernate: Initialize mmu_cr4_features during boot
  x86-32, NUMA: Fix ACPI NUMA init broken by recent x86-64 change
  x86: visws: Fixup irq overhaul fallout

* 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  sched: Clean up rebalance_domains() load-balance interval calculation

* 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86/mrst/vrtc: Fix boot crash in mrst_rtc_init()
  rtc, x86/mrst/vrtc: Fix boot crash in rtc_read_alarm()

* 'irq-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  genirq: Fix cpumask leak in __setup_irq()

* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  perf probe: Fix listing incorrect line number with inline function
  perf probe: Fix to find recursively inlined function
  perf probe: Fix multiple --vars options behavior
  perf probe: Fix to remove redundant close
  perf probe: Fix to ensure function declared file
2011-04-07 12:12:58 -07:00
Linus Torvalds
42933bac11 Merge branch 'for-linus2' of git://git.profusion.mobi/users/lucas/linux-2.6
* 'for-linus2' of git://git.profusion.mobi/users/lucas/linux-2.6:
  Fix common misspellings
2011-04-07 11:14:49 -07:00
Peter Zijlstra
49c022e657 sched: Clean up rebalance_domains() load-balance interval calculation
Instead of the possible multiple-evaluation of num_online_cpus()
in rebalance_domains() that Linus reported, avoid it altogether
in the normal case since it's implemented with a Hamming weight
function over a cpu bitmask which can be darn expensive for those
with big iron.

This also makes it cleaner, smaller and documents the code.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1301991265.2225.12.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-04-05 10:29:36 +02:00
Lucas De Marchi
25985edced Fix common misspellings
Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
2011-03-31 11:26:23 -03:00
Sisir Koppaka
3436ae1298 sched: Fix rebalance interval calculation
The interval for checking scheduling domains if they are due to be
balanced currently depends on boot state NR_CPUS, which may not
accurately reflect the number of online CPUs at the time of check.

Thus replace NR_CPUS with num_online_cpus().

 (ed: Should only affect those who set NR_CPUS really high, such as 4096
      or so :-)

Signed-off-by: Sisir Koppaka <sisir.koppaka@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <AANLkTikqHWid2Q93F5U5Qw5snJH8C5PXoa7J6=6hYO94@mail.gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-03-31 13:00:37 +02:00
Venkatesh Pallipadi
6d1cafd8b5 sched: Resched proper CPU on yield_to()
yield_to_task_fair() has code to resched the CPU of yielding task when the
intention is to resched the CPU of the task that is being yielded to.

Change here fixes the problem and also makes the resched conditional on
rq != p_rq.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1299025701-22168-1-git-send-email-venki@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-03-04 11:14:31 +01:00
Darren Hart
a2f5c9ab79 sched: Allow SCHED_BATCH to preempt SCHED_IDLE tasks
Perform the test for SCHED_IDLE before testing for SCHED_BATCH (and
ensure idle tasks don't preempt idle tasks) so the non-interactive,
but still important, SCHED_BATCH tasks will run in favor of the very
low priority SCHED_IDLE tasks.

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Mike Galbraith <efault@gmx.de>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
LKML-Reference: <1298408674-3130-2-git-send-email-dvhart@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-03-04 11:14:29 +01:00
Peter Zijlstra
866ab43efd sched: Fix the group_imb logic
On a 2*6*2 machine something like:

 taskset -c 3-11 bash -c 'for ((i=0;i<9;i++)) do while :; do :; done & done'

_should_ result in 9 busy CPUs, each running 1 task.

However it didn't quite work reliably, most of the time one cpu of the
second socket (6-11) would be idle and one cpu of the first socket
(0-5) would have two tasks on it.

The group_imb logic is supposed to deal with this and detect when a
particular group is imbalanced (like in our case, 0-2 are idle but 3-5
will have 4 tasks on it).

The detection phase needed a bit of a tweak as it was too weak and
required more than 2 avg weight tasks difference between idle and busy
cpus in the group which won't trigger for our test-case. So cure that
to be one or more avg task weight difference between cpus.

Once the detection phase worked, it was then defeated by the f_b_g()
tests trying to avoid ping-pongs. In particular, this_load >= max_load
triggered because the pulling cpu (the (first) idle cpu in on the
second socket, say 6) would find this_load to be 5 and max_load to be
4 (there'd be 5 tasks running on our socket and only 4 on the other
socket).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nikhil Rao <ncrao@google.com>
Cc: Venkatesh Pallipadi <venki@google.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-23 11:33:57 +01:00
Peter Zijlstra
cc57aa8f4b sched: Clean up some f_b_g() comments
The existing comment tends to grow state (as it already has), split it
up and place it near the actual tests.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nikhil Rao <ncrao@google.com>
Cc: Venkatesh Pallipadi <venki@google.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-23 11:33:56 +01:00
Peter Zijlstra
c186fafe9a sched: Clean up remnants of sd_idle
With the wholesale removal of the sd_idle SMT logic we can clean up
some more.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nikhil Rao <ncrao@google.com>
Cc: Venkatesh Pallipadi <venki@google.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-23 11:33:55 +01:00
Venkatesh Pallipadi
46e49b3836 sched: Wholesale removal of sd_idle logic
sd_idle logic was introduced way back in 2005 (commit 5969fe06),
as an HT optimization.

As per the discussion in the thread here:

  lkml - sched: Resolve sd_idle and first_idle_cpu Catch-22 - v1
  https://patchwork.kernel.org/patch/532501/

The capacity based logic in the load balancer right now handles this
in a much cleaner way, handling more than 2 SMT siblings etc, and sd_idle
does not seem to bring any additional benefits. sd_idle logic also has
some bugs that has performance impact. Here is the patch that removes
the sd_idle logic altogether.

Also, there was a dependency of sched_mc_power_savings == 2, with sd_idle
logic.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Acked-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1297723130-693-1-git-send-email-venki@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-16 13:33:20 +01:00
Mike Galbraith
d95f412200 sched: Add yield_to(task, preempt) functionality
Currently only implemented for fair class tasks.

Add a yield_to_task method() to the fair scheduling class. allowing the
caller of yield_to() to accelerate another thread in it's thread group,
task group.

Implemented via a scheduler hint, using cfs_rq->next to encourage the
target being selected.  We can rely on pick_next_entity to keep things
fair, so noone can accelerate a thread that has already used its fair
share of CPU time.

This also means callers should only call yield_to when they really
mean it.  Calling it too often can result in the scheduler just
ignoring the hint.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201095051.4ddb7738@annuminas.surriel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-03 14:20:33 +01:00
Rik van Riel
ac53db596c sched: Use a buddy to implement yield_task_fair()
Use the buddy mechanism to implement yield_task_fair.  This
allows us to skip onto the next highest priority se at every
level in the CFS tree, unless doing so would introduce gross
unfairness in CPU time distribution.

We order the buddy selection in pick_next_entity to check
yield first, then last, then next.  We need next to be able
to override yield, because it is possible for the "next" and
"yield" task to be different processen in the same sub-tree
of the CFS tree.  When they are, we need to go into that
sub-tree regardless of the "yield" hint, and pick the correct
entity once we get to the right level.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201095103.3a79e92a@annuminas.surriel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-03 14:20:33 +01:00
Rik van Riel
2c13c919d9 sched: Limit the scope of clear_buddies
The clear_buddies function does not seem to play well with the concept
of hierarchical runqueues.  In the following tree, task groups are
represented by 'G', tasks by 'T', next by 'n' and last by 'l'.

     (nl)
    /    \
   G(nl)  G
   / \     \
 T(l) T(n)  T

This situation can arise when a task is woken up T(n), and the previously
running task T(l) is marked last.

When clear_buddies is called from either T(l) or T(n), the next and last
buddies of the group G(nl) will be cleared.  This is not the desired
result, since we would like to be able to find the other type of buddy
in many cases.

This especially a worry when implementing yield_task_fair through the
buddy system.

The fix is simple: only clear the buddy type that the task itself
is indicated to be.  As an added bonus, we stop walking up the tree
when the buddy has already been cleared or pointed elsewhere.

Signed-off-by: Rik van Riel <riel@redhat.coM>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201094837.6b0962a9@annuminas.surriel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-03 14:20:32 +01:00
Rik van Riel
725e7580aa sched: Check the right ->nr_running in yield_task_fair()
With CONFIG_FAIR_GROUP_SCHED, each task_group has its own cfs_rq.
Yielding to a task from another cfs_rq may be worthwhile, since
a process calling yield typically cannot use the CPU right now.

Therefor, we want to check the per-cpu nr_running, not the
cgroup local one.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201094715.798c4f86@annuminas.surriel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-02-03 14:20:32 +01:00
Peter Zijlstra
da7a735e51 sched: Fix switch_from_fair()
When a task is taken out of the fair class we must ensure the vruntime
is properly normalized because when we put it back in it will assume
to be normalized.

The case that goes wrong is when changing away from the fair class
while sleeping. Sleeping tasks have non-normalized vruntime in order
to make sleeper-fairness work. So treat the switch away from fair as a
wakeup and preserve the relative vruntime.

Also update sysrq-n to call the ->switch_{to,from} methods.

Reported-by: Onkalo Samu <samu.p.onkalo@nokia.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-26 12:33:22 +01:00
Paul Turner
f07333bf6e sched: Avoid expensive initial update_cfs_load()
Since cfs->{load_stamp,load_last} are zero-initalized the initial load update
will consider the delta to be 'since the beginning of time'.

This results in a lot of pointless divisions to bring this large period to be
within the sysctl_sched_shares_window.

Fix this by initializing load_stamp to be 1 at cfs_rq initialization, this
allows for an initial load_stamp > load_last which then lets standard idle
truncation proceed.

We avoid spinning (and slightly improve consistency) by fixing delta to be
[period - 1] in this path resulting in a slightly more predictable shares ramp.
(Previously the amount of idle time preserved by the overflow would range between
[period/2,period-1].)

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110122044852.102126037@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-26 12:33:19 +01:00
Paul Turner
6d5ab2932a sched: Simplify update_cfs_shares parameters
Re-visiting this: Since update_cfs_shares will now only ever re-weight an
entity that is a relative parent of the current entity in enqueue_entity; we
can safely issue the account_entity_enqueue relative to that cfs_rq and avoid
the requirement for special handling of the enqueue case in update_cfs_shares.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110122044851.915214637@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-26 12:33:19 +01:00
Paul Turner
05ca62c6ca sched: Use rq->clock_task instead of rq->clock for correctly maintaining load averages
The delta in clock_task is a more fair attribution of how much time a tg has
been contributing load to the current cpu.

While not really important it also means we're more in sync (by magnitude)
with respect to periodic updates (since __update_curr deltas are clock_task
based).

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110122044852.007092349@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-26 12:31:03 +01:00
Paul Turner
b815f1963e sched: Fix/remove redundant cfs_rq checks
Since updates are against an entity's queuing cfs_rq it's not possible to
enter update_cfs_{shares,load} with a NULL cfs_rq.  (Indeed, update_cfs_load
would crash prior to the check if we did anyway since we load is examined
during the initializers).

Also, in the update_cfs_load case there's no point
in maintaining averages for rq->cfs_rq since we don't perform shares
distribution at that level -- NULL check is replaced accordingly.

Thanks to Dan Carpenter for pointing out the deference before NULL check.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110122044851.825284940@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-26 12:31:02 +01:00
Paul Turner
e37b6a7b27 sched: Fix sign under-flows in wake_affine
While care is taken around the zero-point in effective_load to not exceed
the instantaneous rq->weight, it's still possible (e.g. using wake_idx != 0)
for (load + effective_load) to underflow.

In this case the comparing the unsigned values can result in incorrect balanced
decisions.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110122044851.734245014@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-26 12:31:01 +01:00
Yong Zhang
3ff6dcac73 sched: Fix poor interactivity on UP systems due to group scheduler nice tune bug
Michael Witten and Christian Kujau reported that the autogroup
scheduling feature hurts interactivity on their UP systems.

It turns out that this is an older bug in the group scheduling code,
and the wider appeal provided by the autogroup feature exposed it
more prominently.

When on UP with FAIR_GROUP_SCHED enabled, tune shares
only affect tg->shares, but is not reflected in
tg->se->load. The reason is that update_cfs_shares()
does nothing on UP.

So introduce update_cfs_shares() for UP && FAIR_GROUP_SCHED.

This issue was found when enable autogroup scheduling was enabled,
but it is an older bug that also exists on cgroup.cpu on UP.

Reported-and-Tested-by: Michael Witten <mfwitten@gmail.com>
Reported-and-Tested-by: Christian Kujau <christian@nerdbynature.de>
Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Acked-by: Mike Galbraith <efault@gmx.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110124073352.GA24186@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-24 11:47:50 +01:00
Mike Galbraith
d7d8294415 sched: Fix signed unsigned comparison in check_preempt_tick()
Signed unsigned comparison may lead to superfluous resched if leftmost
is right of the current task, wasting a few cycles, and inadvertently
_lengthening_ the current task's slice.

Reported-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1294202477.9384.5.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-18 15:09:44 +01:00
Paul Turner
977dda7c9b sched: Update effective_load() to use global share weights
Previously effective_load would approximate the global load weight present on
a group taking advantage of:

entity_weight = tg->shares ( lw / global_lw ), where entity_weight was provided
by tg_shares_up.

This worked (approximately) for an 'empty' (at tg level) cpu since we would
place boost load representative of what a newly woken task would receive.

However, now that load is instantaneously updated this assumption is no longer
true and the load calculation is rather incorrect in this case.

Fix this (and improve the general case) by re-writing effective_load to take
advantage of the new shares distribution code.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110115015817.069769529@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2011-01-18 15:09:38 +01:00
Paul Turner
19e5eebb8e sched: Fix interactivity bug by charging unaccounted run-time on entity re-weight
Mike Galbraith reported poor interactivity[*] when the new shares distribution
code was combined with autogroups.

The root cause turns out to be a mis-ordering of accounting accrued execution
time and shares updates.  Since update_curr() is issued hierarchically,
updating the parent entity weights to reflect child enqueue/dequeue results in
the parent's unaccounted execution time then being accrued (vs vruntime) at the
new weight as opposed to the weight present at accumulation.

While this doesn't have much effect on processes with timeslices that cross a
tick, it is particularly problematic for an interactive process (e.g. Xorg)
which incurs many (tiny) timeslices.  In this scenario almost all updates are
at dequeue which can result in significant fairness perturbation (especially if
it is the only thread, resulting in potential {tg->shares, MIN_SHARES}
transitions).

Correct this by ensuring unaccounted time is accumulated prior to manipulating
an entity's weight.

[*] http://xkcd.com/619/ is perversely Nostradamian here.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20101216031038.159704378@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-12-19 16:36:30 +01:00
Paul Turner
43365bd7ff sched: Move periodic share updates to entity_tick()
Long running entities that do not block (dequeue) require periodic updates to
maintain accurate share values.  (Note: group entities with several threads are
quite likely to be non-blocking in many circumstances).

By virtue of being long-running however, we will see entity ticks (otherwise
the required update occurs in dequeue/put and we are done).  Thus we can move
the detection (and associated work) for these updates into the periodic path.

This restores the 'atomicity' of update_curr() with respect to accounting.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101216031038.067028969@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-12-19 16:36:22 +01:00
Ingo Molnar
8e9255e6a2 Merge branch 'linus' into sched/core
Merge reason: we want to queue up dependent cleanup

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-12-08 20:15:29 +01:00
Ingo Molnar
22a867d817 Merge commit 'v2.6.37-rc3' into sched/core
Merge reason: Pick up latest fixes.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-26 15:05:21 +01:00
Peter Zijlstra
70caf8a6c1 sched: Fix UP build breakage
The recent cgroup-scheduling rework caused a UP build problem.

Cc: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-23 10:29:07 +01:00
Paul Turner
d6b5591829 sched: Allow update_cfs_load() to update global load
Refactor the global load updates from update_shares_cpu() so that
update_cfs_load() can update global load when it is more than ~10%
out of sync.

The new global_load parameter allows us to force an update, regardless of
the error factor so that we can synchronize w/ update_shares().

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234938.377473595@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:50 +01:00
Paul Turner
3b3d190ec3 sched: Implement demand based update_cfs_load()
When the system is busy, dilation of rq->next_balance makes lb->update_shares()
insufficiently frequent for threads which don't sleep (no dequeue/enqueue
updates).  Adjust for this by making demand based updates based on the
accumulation of execution time sufficient to wrap our averaging window.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234938.291159744@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:49 +01:00
Paul Turner
c66eaf619c sched: Update shares on idle_balance
Since shares updates are no longer expensive and effectively local, update them
at idle_balance().  This allows us to more quickly redistribute shares to
another cpu when our load becomes idle.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234938.204191702@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:49 +01:00
Paul Turner
a7a4f8a752 sched: Add sysctl_sched_shares_window
Introduce a new sysctl for the shares window and disambiguate it from
sched_time_avg.

A 10ms window appears to be a good compromise between accuracy and performance.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234938.112173964@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:49 +01:00
Paul Turner
67e86250f8 sched: Introduce hierarchal order on shares update list
Avoid duplicate shares update calls by ensuring children always appear before
parents in rq->leaf_cfs_rq_list.

This allows us to do a single in-order traversal for update_shares().

Since we always enqueue in bottom-up order this reduces to 2 cases:

1) Our parent is already in the list, e.g.

   root
     \
      b
      /\
      c d* (root->b->c already enqueued)

Since d's parent is enqueued we push it to the head of the list, implicitly ahead of b.

2) Our parent does not appear in the list (or we have no parent)

In this case we enqueue to the tail of the list, if our parent is subsequently enqueued
(bottom-up) it will appear to our right by the same rule.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234938.022488865@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:48 +01:00
Paul Turner
e33078baa4 sched: Fix update_cfs_load() synchronization
Using cfs_rq->nr_running is not sufficient to synchronize update_cfs_load with
the put path since nr_running accounting occurs at deactivation.

It's also not safe to make the removal decision based on load_avg as this fails
with both high periods and low shares.  Resolve this by clipping history after
4 periods without activity.

Note: the above will always occur from update_shares() since in the
last-task-sleep-case that task will still be cfs_rq->curr when update_cfs_load
is called.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234937.933428187@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:48 +01:00
Paul Turner
f0d7442a59 sched: Fix load corruption from update_cfs_shares()
As part of enqueue_entity both a new entity weight and its contribution to the
queuing cfs_rq / rq are updated.  Since update_cfs_shares will only update the
queueing weights when the entity is on_rq (which in this case it is not yet),
there's a dependency loop here:

update_cfs_shares needs account_entity_enqueue to update cfs_rq->load.weight
account_entity_enqueue needs the updated weight for the queuing cfs_rq load[*]

Fix this and avoid spurious dequeue/enqueues by issuing update_cfs_shares as
if we had accounted the enqueue already.

This was also resulting in rq->load corruption previously.

[*]: this dependency also exists when using the group cfs_rq w/
     update_cfs_shares as the weight of the enqueued entity changes
     without the load being updated.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234937.844900206@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:47 +01:00
Peter Zijlstra
9e3081ca61 sched: Make tg_shares_up() walk on-demand
Make tg_shares_up() use the active cgroup list, this means we cannot
do a strict bottom-up walk of the hierarchy, but assuming its a very
wide tree with a small number of active groups it should be a win.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234937.754159484@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:47 +01:00
Peter Zijlstra
3d4b47b4b0 sched: Implement on-demand (active) cfs_rq list
Make certain load-balance actions scale per number of active cgroups
instead of the number of existing cgroups.

This makes wakeup/sleep paths more expensive, but is a win for systems
where the vast majority of existing cgroups are idle.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234937.666535048@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:47 +01:00
Peter Zijlstra
2069dd75c7 sched: Rewrite tg_shares_up)
By tracking a per-cpu load-avg for each cfs_rq and folding it into a
global task_group load on each tick we can rework tg_shares_up to be
strictly per-cpu.

This should improve cpu-cgroup performance for smp systems
significantly.

[ Paul: changed to use queueing cfs_rq + bug fixes ]

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234937.580480400@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:27:46 +01:00
Nikhil Rao
d5ad140bc1 sched: Fix idle balancing
An earlier commit reverts idle balancing throttling reset to fix a 30%
regression in volanomark throughput. We still need to reset idle_stamp
when we pull a task in newidle balance.

Reported-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Nikhil Rao <ncrao@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1290022924-3548-1-git-send-email-ncrao@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:12:33 +01:00
Alex Shi
b5482cfa1c sched: Fix volanomark performance regression
Commit fab4762 triggers excessive idle balancing, causing a ~30% loss in
volanomark throughput. Remove idle balancing throttle reset.

Originally-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Acked-by: Nikhil Rao <ncrao@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1289928732.5169.211.camel@maggy.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-18 13:11:43 +01:00
Peter Zijlstra
1e5a74059f sched: Fix cross-sched-class wakeup preemption
Instead of dealing with sched classes inside each check_preempt_curr()
implementation, pull out this logic into the generic wakeup preemption
path.

This fixes a hang in KVM (and others) where we are waiting for the
stop machine thread to run ...

Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Tested-by: Marcelo Tosatti <mtosatti@redhat.com>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1288891946.2039.31.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-11 14:37:23 +01:00
Suresh Siddha
aae6d3ddd8 sched: Use group weight, idle cpu metrics to fix imbalances during idle
Currently we consider a sched domain to be well balanced when the imbalance
is less than the domain's imablance_pct. As the number of cores and threads
are increasing, current values of imbalance_pct (for example 25% for a
NUMA domain) are not enough to detect imbalances like:

a) On a WSM-EP system (two sockets, each having 6 cores and 12 logical threads),
24 cpu-hogging tasks get scheduled as 13 on one socket and 11 on another
socket. Leading to an idle HT cpu.

b) On a hypothetial 2 socket NHM-EX system (each socket having 8 cores and
16 logical threads), 16 cpu-hogging tasks can get scheduled as 9 on one
socket and 7 on another socket. Leaving one core in a socket idle
whereas in another socket we have a core having both its HT siblings busy.

While this issue can be fixed by decreasing the domain's imbalance_pct
(by making it a function of number of logical cpus in the domain), it
can potentially cause more task migrations across sched groups in an
overloaded case.

Fix this by using imbalance_pct only during newly_idle and busy
load balancing. And during idle load balancing, check if there
is an imbalance in number of idle cpu's across the busiest and this
sched_group or if the busiest group has more tasks than its weight that
the idle cpu in this_group can pull.

Reported-by: Nikhil Rao <ncrao@google.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1284760952.2676.11.camel@sbsiddha-MOBL3.sc.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-11-10 23:13:56 +01:00
Linus Torvalds
37542b6a7e Merge branch 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  sched_stat: Update sched_info_queue/dequeue() code comments
  sched, cgroup: Fixup broken cgroup movement
2010-10-29 08:05:33 -07:00
Peter Zijlstra
b2b5ce022a sched, cgroup: Fixup broken cgroup movement
Dima noticed that we fail to correct the ->vruntime of sleeping tasks
when we move them between cgroups.

Reported-by: Dima Zavin <dima@android.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Mike Galbraith <efault@gmx.de>
LKML-Reference: <1287150604.29097.1513.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-10-22 14:16:45 +02:00
Linus Torvalds
bc4016f481 Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (29 commits)
  sched: Export account_system_vtime()
  sched: Call tick_check_idle before __irq_enter
  sched: Remove irq time from available CPU power
  sched: Do not account irq time to current task
  x86: Add IRQ_TIME_ACCOUNTING
  sched: Add IRQ_TIME_ACCOUNTING, finer accounting of irq time
  sched: Add a PF flag for ksoftirqd identification
  sched: Consolidate account_system_vtime extern declaration
  sched: Fix softirq time accounting
  sched: Drop group_capacity to 1 only if local group has extra capacity
  sched: Force balancing on newidle balance if local group has capacity
  sched: Set group_imb only a task can be pulled from the busiest cpu
  sched: Do not consider SCHED_IDLE tasks to be cache hot
  sched: Drop all load weight manipulation for RT tasks
  sched: Create special class for stop/migrate work
  sched: Unindent labels
  sched: Comment updates: fix default latency and granularity numbers
  tracing/sched: Add sched_pi_setprio tracepoint
  sched: Give CPU bound RT tasks preference
  sched: Try not to migrate higher priority RT tasks
  ...
2010-10-21 12:55:43 -07:00
Venkatesh Pallipadi
aa48380851 sched: Remove irq time from available CPU power
The idea was suggested by Peter Zijlstra here:

  http://marc.info/?l=linux-kernel&m=127476934517534&w=2

irq time is technically not available to the tasks running on the CPU.
This patch removes irq time from CPU power piggybacking on
sched_rt_avg_update().

Tested this by keeping CPU X busy with a network intensive task having 75%
oa a single CPU irq processing (hard+soft) on a 4-way system. And start seven
cycle soakers on the system. Without this change, there will be two tasks on
each CPU. With this change, there is a single task on irq busy CPU X and
remaining 7 tasks are spread around among other 3 CPUs.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1286237003-12406-8-git-send-email-venki@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-10-18 20:52:27 +02:00
Venkatesh Pallipadi
305e6835e0 sched: Do not account irq time to current task
Scheduler accounts both softirq and interrupt processing times to the
currently running task. This means, if the interrupt processing was
for some other task in the system, then the current task ends up being
penalized as it gets shorter runtime than otherwise.

Change sched task accounting to acoount only actual task time from
currently running task. Now update_curr(), modifies the delta_exec to
depend on rq->clock_task.

Note that this change only handles CONFIG_IRQ_TIME_ACCOUNTING case. We can
extend this to CONFIG_VIRT_CPU_ACCOUNTING with minimal effort. But, thats
for later.

This change will impact scheduling behavior in interrupt heavy conditions.

Tested on a 4-way system with eth0 handled by CPU 2 and a network heavy
task (nc) running on CPU 3 (and no RSS/RFS). With that I have CPU 2
spending 75%+ of its time in irq processing. CPU 3 spending around 35%
time running nc task.

Now, if I run another CPU intensive task on CPU 2, without this change
/proc/<pid>/schedstat shows 100% of time accounted to this task. With this
change, it rightly shows less than 25% accounted to this task as remaining
time is actually spent on irq processing.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1286237003-12406-7-git-send-email-venki@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2010-10-18 20:52:26 +02:00