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  1. 14 8月, 2011 5 次提交
  3. 22 7月, 2011 6 次提交
  5. 21 7月, 2011 1 次提交
  7. 01 7月, 2011 1 次提交
  9. 28 5月, 2011 1 次提交
  11. 20 5月, 2011 1 次提交
  13. 04 5月, 2011 1 次提交
  15. 19 4月, 2011 2 次提交
    • V
      sched: Next buddy hint on sleep and preempt path · 2f36825b
      由 Venkatesh Pallipadi 提交于 
      When a task in a taskgroup sleeps, pick_next_task starts all the way back at
the root and picks the task/taskgroup with the min vruntime across all
runnable tasks.

But when there are many frequently sleeping tasks across different taskgroups,
it makes better sense to stay with same taskgroup for its slice period (or
until all tasks in the taskgroup sleeps) instead of switching cross taskgroup
on each sleep after a short runtime.

This helps specifically where taskgroups corresponds to a process with
multiple threads. The change reduces the number of CR3 switches in this case.

Example:

Two taskgroups with 2 threads each which are running for 2ms and
sleeping for 1ms. Looking at sched:sched_switch shows:

BEFORE: taskgroup_1 threads [5004, 5005], taskgroup_2 threads [5016, 5017]
      cpu-soaker-5004  [003]  3683.391089
      cpu-soaker-5016  [003]  3683.393106
      cpu-soaker-5005  [003]  3683.395119
      cpu-soaker-5017  [003]  3683.397130
      cpu-soaker-5004  [003]  3683.399143
      cpu-soaker-5016  [003]  3683.401155
      cpu-soaker-5005  [003]  3683.403168
      cpu-soaker-5017  [003]  3683.405170

AFTER: taskgroup_1 threads [21890, 21891], taskgroup_2 threads [21934, 21935]
      cpu-soaker-21890 [003]   865.895494
      cpu-soaker-21935 [003]   865.897506
      cpu-soaker-21934 [003]   865.899520
      cpu-soaker-21935 [003]   865.901532
      cpu-soaker-21934 [003]   865.903543
      cpu-soaker-21935 [003]   865.905546
      cpu-soaker-21891 [003]   865.907548
      cpu-soaker-21890 [003]   865.909560
      cpu-soaker-21891 [003]   865.911571
      cpu-soaker-21890 [003]   865.913582
      cpu-soaker-21891 [003]   865.915594
      cpu-soaker-21934 [003]   865.917606

Similar problem is there when there are multiple taskgroups and say a task A
preempts currently running task B of taskgroup_1. On schedule, pick_next_task
can pick an unrelated task on taskgroup_2. Here it would be better to give some
preference to task B on pick_next_task.

A simple (may be extreme case) benchmark I tried was tbench with 2 tbench
client processes with 2 threads each running on a single CPU. Avg throughput
across 5 50 sec runs was:

 BEFORE: 105.84 MB/sec
 AFTER:  112.42 MB/sec
Signed-off-by: NVenkatesh Pallipadi <venki@google.com>
Acked-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1302802253-25760-1-git-send-email-venki@google.comSigned-off-by: NIngo Molnar <mingo@elte.hu>
      2f36825b
    • V
      sched: Make set_*_buddy() work on non-task entities · 69c80f3e
      由 Venkatesh Pallipadi 提交于 
      Make set_*_buddy() work on non-task sched_entity, to facilitate the
use of next_buddy to cache a group entity in cases where one of the
tasks within that entity sleeps or gets preempted.

set_skip_buddy() was incorrectly comparing the policy of task that is
yielding to be not equal to SCHED_IDLE. Yielding should happen even
when task yielding is SCHED_IDLE. This change removes the policy check
on the yielding task.
Signed-off-by: NVenkatesh Pallipadi <venki@google.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1302744070-30079-2-git-send-email-venki@google.comSigned-off-by: NIngo Molnar <mingo@elte.hu>
      69c80f3e
  17. 14 4月, 2011 3 次提交
  19. 11 4月, 2011 5 次提交
    • P
      sched: Avoid using sd->level · a6c75f2f
      由 Peter Zijlstra 提交于 
      Don't use sd->level for identifying properties of the domain.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110407122942.350174079@chello.nlSigned-off-by: NIngo Molnar <mingo@elte.hu>
      a6c75f2f
    • P
      sched: Dynamically allocate sched_domain/sched_group data-structures · dce840a0
      由 Peter Zijlstra 提交于 
      Instead of relying on static allocations for the sched_domain and
sched_group trees, dynamically allocate and RCU free them.

Allocating this dynamically also allows for some build_sched_groups()
simplification since we can now (like with other simplifications) rely
on the sched_domain tree instead of hard-coded knowledge.

One tricky to note is that detach_destroy_domains() needs to hold
rcu_read_lock() over the entire tear-down, per-cpu is not sufficient
since that can lead to partial sched_group existance (could possibly
be solved by doing the tear-down backwards but this is much more
robust).

A concequence of the above is that we can no longer print the
sched_domain debug stuff from cpu_attach_domain() since that might now
run with preemption disabled (due to classic RCU etc.) and
sched_domain_debug() does some GFP_KERNEL allocations.

Another thing to note is that we now fully rely on normal RCU and not
RCU-sched, this is because with the new and exiting RCU flavours we
grew over the years BH doesn't necessarily hold off RCU-sched grace
periods (-rt is known to break this). This would in fact already cause
us grief since we do sched_domain/sched_group iterations from softirq
context.

This patch is somewhat larger than I would like it to be, but I didn't
find any means of shrinking/splitting this.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110407122942.245307941@chello.nlSigned-off-by: NIngo Molnar <mingo@elte.hu>
      dce840a0
    • S
      sched: Eliminate dead code from wakeup_gran() · f4ad9bd2
      由 Shaohua Li 提交于 
      calc_delta_fair() checks NICE_0_LOAD already, delete duplicate check.

Signed-off-by: Shaohua Li<shaohua.li@intel.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Link: http://lkml.kernel.org/r/1302238389.3981.92.camel@sli10-conroeSigned-off-by: NIngo Molnar <mingo@elte.hu>
      f4ad9bd2
    • K
      sched: Fix erroneous all_pinned logic · b30aef17
      由 Ken Chen 提交于 
      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: NKen Chen <kenchen@google.com>
Cc: stable@kernel.org
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/BANLkTi=ernzNawaR5tJZEsV_QVnfxqXmsQ@mail.gmail.comSigned-off-by: NIngo Molnar <mingo@elte.hu>
      b30aef17
    • K
      sched: Fix sched-domain avg_load calculation · b0432d8f
      由 Ken Chen 提交于 
      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: NKen Chen <kenchen@google.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/20110408002322.3A0D812217F@elm.corp.google.comSigned-off-by: NIngo Molnar <mingo@elte.hu>
      b0432d8f
  21. 05 4月, 2011 1 次提交
  23. 31 3月, 2011 2 次提交
  25. 04 3月, 2011 2 次提交
  27. 23 2月, 2011 3 次提交
    • P
      sched: Fix the group_imb logic · 866ab43e
      由 Peter Zijlstra 提交于 
      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: NPeter 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: NIngo Molnar <mingo@elte.hu>
      866ab43e
    • P
      sched: Clean up some f_b_g() comments · cc57aa8f
      由 Peter Zijlstra 提交于 
      The existing comment tends to grow state (as it already has), split it
up and place it near the actual tests.
Signed-off-by: NPeter 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: NIngo Molnar <mingo@elte.hu>
      cc57aa8f
    • P
      sched: Clean up remnants of sd_idle · c186fafe
      由 Peter Zijlstra 提交于 
      With the wholesale removal of the sd_idle SMT logic we can clean up
some more.
Signed-off-by: NPeter 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: NIngo Molnar <mingo@elte.hu>
      c186fafe
  29. 16 2月, 2011 1 次提交
  31. 03 2月, 2011 4 次提交
    • M
      sched: Add yield_to(task, preempt) functionality · d95f4122
      由 Mike Galbraith 提交于 
      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: NRik van Riel <riel@redhat.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NMike Galbraith <efault@gmx.de>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201095051.4ddb7738@annuminas.surriel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      d95f4122
    • R
      sched: Use a buddy to implement yield_task_fair() · ac53db59
      由 Rik van Riel 提交于 
      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: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201095103.3a79e92a@annuminas.surriel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      ac53db59
    • R
      sched: Limit the scope of clear_buddies · 2c13c919
      由 Rik van Riel 提交于 
      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: NRik van Riel <riel@redhat.coM>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201094837.6b0962a9@annuminas.surriel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      2c13c919
    • R
      sched: Check the right ->nr_running in yield_task_fair() · 725e7580
      由 Rik van Riel 提交于 
      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: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110201094715.798c4f86@annuminas.surriel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      725e7580
  33. 26 1月, 2011 1 次提交
    • P
      sched: Fix switch_from_fair() · da7a735e
      由 Peter Zijlstra 提交于 
      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: NOnkalo Samu <samu.p.onkalo@nokia.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      da7a735e