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| author | Ingo Molnar <mingo@elte.hu> | 2010-09-12 08:14:52 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2010-09-13 20:17:11 +0200 |
| commit | 0bf377bbb0bea6130f35613491887cc622e42a8b (patch) | |
| tree | 1ecb56fb6195dcdb673ef3a08390b98e54f4f726 | |
| parent | 49553c2ef88749dd502687f4eb9c258bb10a4f44 (diff) | |
| download | linux-0bf377bbb0bea6130f35613491887cc622e42a8b.tar.gz linux-0bf377bbb0bea6130f35613491887cc622e42a8b.tar.bz2 linux-0bf377bbb0bea6130f35613491887cc622e42a8b.zip | |
sched: Improve latencies under load by decreasing minimum scheduling granularity
Mathieu reported bad latencies with make -j10 kind of kbuild
workloads - which is mostly caused by us scheduling with a
too coarse granularity.
Reduce the minimum granularity some more, to make sure we
can meet the latency target.
I got the following results (make -j10 kbuild load, average of 3
runs):
vanilla:
maximum latency: 38278.9 µs
average latency: 7730.1 µs
patched:
maximum latency: 22702.1 µs
average latency: 6684.8 µs
Mathieu also measured it:
|
| * wakeup-latency.c (SIGEV_THREAD) with make -j10
|
| - Mainline 2.6.35.2 kernel
|
| maximum latency: 45762.1 µs
| average latency: 7348.6 µs
|
| - With only Peter's smaller min_gran (shown below):
|
| maximum latency: 29100.6 µs
| average latency: 6684.1 µs
|
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <AANLkTi=8m4g01wZPacySoF7U0PevTNVgJoZZrHiUD-pN@mail.gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
| -rw-r--r-- | kernel/sched_fair.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 9b5b4f86b742..a171138a9402 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -54,13 +54,13 @@ enum sched_tunable_scaling sysctl_sched_tunable_scaling * Minimal preemption granularity for CPU-bound tasks: * (default: 2 msec * (1 + ilog(ncpus)), units: nanoseconds) */ -unsigned int sysctl_sched_min_granularity = 2000000ULL; -unsigned int normalized_sysctl_sched_min_granularity = 2000000ULL; +unsigned int sysctl_sched_min_granularity = 750000ULL; +unsigned int normalized_sysctl_sched_min_granularity = 750000ULL; /* * is kept at sysctl_sched_latency / sysctl_sched_min_granularity */ -static unsigned int sched_nr_latency = 3; +static unsigned int sched_nr_latency = 8; /* * After fork, child runs first. If set to 0 (default) then |