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sched: Improve scalability via 'CPU buddies', which withstand random perturbations

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Traversing an entire package is not only expensive, it also leads to tasks
bouncing all over a partially idle and possible quite large package.  Fix
that up by assigning a 'buddy' CPU to try to motivate.  Each buddy may try
to motivate that one other CPU, if it's busy, tough, it may then try its
SMT sibling, but that's all this optimization is allowed to cost.

Sibling cache buddies are cross-wired to prevent bouncing.

4 socket 40 core + SMT Westmere box, single 30 sec tbench runs, higher is better:

 clients     1       2       4        8       16       32       64      128
 ..........................................................................
 pre        30      41     118      645     3769     6214    12233    14312
 post      299     603    1211     2418     4697     6847    11606    14557

A nice increase in performance.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1339471112.7352.32.camel@marge.simpson.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Mike Galbraith
2012-06-12 05:18:32 +02:00
committed by Ingo Molnar
parent a1cd2b13f7
commit 970e178985
3 changed files with 46 additions and 22 deletions
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1
include/linux/sched.h
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@@ -949,6 +949,7 @@ struct sched_domain {
unsigned int smt_gain;
int flags; /* See SD_* */
int level;
int idle_buddy; /* cpu assigned to select_idle_sibling() */
/* Runtime fields. */
unsigned long last_balance; /* init to jiffies. units in jiffies */