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| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2008-06-27 13:41:39 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-06-27 14:31:47 +0200 |
| commit | f5bfb7d9ff73d72ee4f2f4830a6f0c9088d00f92 (patch) | |
| tree | 402e8caaef4d3f0c26a52b171e04dbb67ea08cfa | |
| parent | f1d239f73200a5803a89e5929fb3abc1596b7589 (diff) | |
| download | lwn-f5bfb7d9ff73d72ee4f2f4830a6f0c9088d00f92.tar.gz lwn-f5bfb7d9ff73d72ee4f2f4830a6f0c9088d00f92.zip | |
sched: bias effective_load() error towards failing wake_affine().
Measurement shows that the difference between cgroup:/ and cgroup:/foo
wake_affine() results is that the latter succeeds significantly more.
Therefore bias the calculations towards failing the test.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
| -rw-r--r-- | kernel/sched_fair.c | 28 | ||||
| -rw-r--r-- | kernel/sched_features.h | 1 |
2 files changed, 29 insertions, 0 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index e87f1a52f625..9bcc0030a58b 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1074,6 +1074,27 @@ static inline int wake_idle(int cpu, struct task_struct *p) static const struct sched_class fair_sched_class; #ifdef CONFIG_FAIR_GROUP_SCHED +/* + * effective_load() calculates the load change as seen from the root_task_group + * + * Adding load to a group doesn't make a group heavier, but can cause movement + * of group shares between cpus. Assuming the shares were perfectly aligned one + * can calculate the shift in shares. + * + * The problem is that perfectly aligning the shares is rather expensive, hence + * we try to avoid doing that too often - see update_shares(), which ratelimits + * this change. + * + * We compensate this by not only taking the current delta into account, but + * also considering the delta between when the shares were last adjusted and + * now. + * + * We still saw a performance dip, some tracing learned us that between + * cgroup:/ and cgroup:/foo balancing the number of affine wakeups increased + * significantly. Therefore try to bias the error in direction of failing + * the affine wakeup. + * + */ static long effective_load(struct task_group *tg, int cpu, long wl, long wg) { @@ -1084,6 +1105,13 @@ static long effective_load(struct task_group *tg, int cpu, return wl; /* + * By not taking the decrease of shares on the other cpu into + * account our error leans towards reducing the affine wakeups. + */ + if (!wl && sched_feat(ASYM_EFF_LOAD)) + return wl; + + /* * Instead of using this increment, also add the difference * between when the shares were last updated and now. */ diff --git a/kernel/sched_features.h b/kernel/sched_features.h index 7d616d2a2a3f..862b06bd560a 100644 --- a/kernel/sched_features.h +++ b/kernel/sched_features.h @@ -10,3 +10,4 @@ SCHED_FEAT(DOUBLE_TICK, 0) SCHED_FEAT(ASYM_GRAN, 1) SCHED_FEAT(LB_BIAS, 0) SCHED_FEAT(LB_WAKEUP_UPDATE, 1) +SCHED_FEAT(ASYM_EFF_LOAD, 1) |