linux.git/kernel/sched_features.h, branch v3.0-rc7

sched: Move the second half of ttwu() to the remote cpu

2011-04-14T06:52:41+00:00

Now that we've removed the rq->lock requirement from the first part of
ttwu() and can compute placement without holding any rq->lock, ensure
we execute the second half of ttwu() on the actual cpu we want the
task to run on.

This avoids having to take rq->lock and doing the task enqueue
remotely, saving lots on cacheline transfers.

As measured using: http://oss.oracle.com/~mason/sembench.c

  $ for i in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor ; do echo performance > $i; done
  $ echo 4096 32000 64 128 > /proc/sys/kernel/sem
  $ ./sembench -t 2048 -w 1900 -o 0

  unpatched: run time 30 seconds 647278 worker burns per second
  patched:   run time 30 seconds 816715 worker burns per second

Reviewed-by: Frank Rowand 
Cc: Mike Galbraith 
Cc: Nick Piggin 
Cc: Linus Torvalds 
Cc: Andrew Morton 
Signed-off-by: Ingo Molnar 
Signed-off-by: Peter Zijlstra 
Link: http://lkml.kernel.org/r/20110405152729.515897185@chello.nl

sched: Rewrite tg_shares_up)

2010-11-18T12:27:46+00:00

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 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20101115234937.580480400@google.com>
Signed-off-by: Ingo Molnar

sched: Remove irq time from available CPU power

2010-10-18T18:52:27+00:00

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 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1286237003-12406-8-git-send-email-venki@google.com>
Signed-off-by: Ingo Molnar

sched: Remove ASYM_GRAN feature

2010-03-11T17:32:53+00:00

This features has been enabled for quite a while, after testing showed that
easing preemption for light tasks was harmful to high priority threads.

Remove the feature flag.

Signed-off-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1268301675.6785.44.camel@marge.simson.net>
Signed-off-by: Ingo Molnar

sched: Remove SYNC_WAKEUPS feature

2010-03-11T17:32:53+00:00

Sync wakeups are critical functionality with a long history.  Remove it, we don't
need the branch or icache footprint.

Signed-off-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1268301817.6785.47.camel@marge.simson.net>
Signed-off-by: Ingo Molnar

sched: Remove WAKEUP_SYNC feature

2010-03-11T17:32:52+00:00

This feature never earned its keep, remove it.

Signed-off-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1268301591.6785.42.camel@marge.simson.net>
Signed-off-by: Ingo Molnar

sched: Remove FAIR_SLEEPERS feature

2010-03-11T17:32:52+00:00

Our preemption model relies too heavily on sleeper fairness to disable it
without dire consequences.  Remove the feature, and save a branch or two.

Signed-off-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1268301520.6785.40.camel@marge.simson.net>
Signed-off-by: Ingo Molnar

sched: Remove NORMALIZED_SLEEPER

2010-03-11T17:32:52+00:00

This feature hasn't been enabled in a long time, remove effectively dead code.

Signed-off-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1268301447.6785.38.camel@marge.simson.net>
Signed-off-by: Ingo Molnar

sched: Remove avg_overlap

2010-03-11T17:32:50+00:00

Both avg_overlap and avg_wakeup had an inherent problem in that their accuracy
was detrimentally affected by cross-cpu wakeups, this because we are missing
the necessary call to update_curr().  This can't be fixed without increasing
overhead in our already too fat fastpath.

Additionally, with recent load balancing changes making us prefer to place tasks
in an idle cache domain (which is good for compute bound loads), communicating
tasks suffer when a sync wakeup, which would enable affine placement, is turned
into a non-sync wakeup by SYNC_LESS.  With one task on the runqueue, wake_affine()
rejects the affine wakeup request, leaving the unfortunate where placed, taking
frequent cache misses.

Remove it, and recover some fastpath cycles.

Signed-off-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1268301121.6785.30.camel@marge.simson.net>
Signed-off-by: Ingo Molnar

sched: Remove avg_wakeup

2010-03-11T17:32:50+00:00

Testing the load which led to this heuristic (nfs4 kbuild) shows that it has
outlived it's usefullness.  With intervening load balancing changes, I cannot
see any difference with/without, so recover there fastpath cycles.

Signed-off-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1268301062.6785.29.camel@marge.simson.net>
Signed-off-by: Ingo Molnar