Re: [REPORT] cfs-v5 vs sd-0.46

From: Ingo Molnar
Date: Tue Apr 24 2007 - 04:25:09 EST

* Michael Gerdau <mgd@xxxxxxxxxxxx> wrote:

> > so to be totally 'fair' and get the same rescheduling 'granularity'
> > you should probably lower CFS's sched_granularity_ns to 2 msecs.
> I'll change default nice in cfs to -10.
> I'm also happy to adjust /proc/sys/kernel/sched_granularity_ns to
> 2msec. However checking /proc/sys/kernel/rr_interval reveals it is 16
> (msec) on my system.

ah, yeah - there due to the SMP rule in SD:

rr_interval *= 1 + ilog2(num_online_cpus());

and you have a 2-CPU system, so you get 8msec*2 == 16 msecs default
interval. I find this a neat solution and i have talked to Con about
this already and i'll adopt Con's idea in CFS too. Nevertheless, despite
the settings, SD seems to be rescheduling every 6-7 msecs, while CFS
reschedules only every 13 msecs.

Here i'm assuming that the vmstats are directly comparable: that your
number-crunchers behave the same during the full runtime - is that
correct? (If not then the vmstat result should be run at roughly the
same type of "stage" of the workload, on all the schedulers.)

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