Messages in this thread Patch in this message | | | Date | Mon, 13 Sep 2010 20:23:55 +0200 | From | Ingo Molnar <> | Subject | [PATCH] sched: Improve latencies under load by decreasing minimum scheduling granularity |
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* Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> * Ingo Molnar (mingo@elte.hu) wrote: > > > > * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > > > > > * Linus Torvalds (torvalds@linux-foundation.org) wrote: > > > > On Mon, Sep 13, 2010 at 9:16 AM, Mathieu Desnoyers > > > > <mathieu.desnoyers@efficios.com> wrote: > > > > > > > > > > OK, the long IRC discussions we just had convinced me that the current scheme > > > > > takes things into account by adapting the granularity dynamically, but also got > > > > > me to notice that check_preempt seems to compare vruntime with wall time, which > > > > > is utterly incorrect. So maybe all my patch was doing was to expose this bug: > > > > > > > > Do you have latency numbers for this patch? > > > > > > Sure, see below, > > > > > > In addition to this patch, [...] > > > > Note, which is a NOP for your latency workload. > > > > > [...] I also used Peter's approach of reducing the minimum granularity > > > > Ok, that's the very first patch i sent yesterday morning - so we also > > have my numbers that it reduces latencies. > > > > To move things along i'll apply it with your Reported-by and Acked-by > > line, ok? > > > > We can also work on the other, more complex things after that, but first > > lets make some progress on the latency front ... > > Yep, that's fine with me. > > Thanks!
You are welcome!
Linus, Mathieu, you can test the granularity reduction patch via:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git sched/urgent
Patch also attached below.
Note, i'd like to keep this separate from the check_preempt() change - which only affects reniced tasks and isnt essential to these tests. (we want such things to be in separate commits, for bisectability)
Thanks,
Ingo
------------------> Ingo Molnar (1): sched: Improve latencies under load by decreasing minimum scheduling granularity
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 9b5b4f8..a171138 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
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