From: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
To: Peter Williams <pwil3058@bigpond.net.au>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
Con Kolivas <kernel@kolivas.org>,
mingo@elte.hu, nickpiggin@yahoo.com.au,
linux-kernel@vger.kernel.org
Subject: Re: smp 'nice' bias support breaks scheduler behavior
Date: Thu, 26 Jan 2006 15:56:23 -0800 [thread overview]
Message-ID: <20060126155623.A19789@unix-os.sc.intel.com> (raw)
In-Reply-To: <43D95D04.8050802@bigpond.net.au>; from pwil3058@bigpond.net.au on Fri, Jan 27, 2006 at 10:36:36AM +1100
On Fri, Jan 27, 2006 at 10:36:36AM +1100, Peter Williams wrote:
> Con Kolivas wrote:
> > On Thursday 26 January 2006 21:52, Siddha, Suresh B wrote:
> >>>[PATCH] sched: implement nice support across physical cpus on SMP
> >>
> >>I don't see imbalance calculations in find_busiest_group() take
> >>prio_bias into account. This will result in wrong imbalance value and
> >>will cause issues.
> > in 2.6.16-rc1:
> >
> > find_busiest_group(....
> >
> > load = __target_load(i, load_idx, idle);
> > else
> > load = __source_load(i, load_idx, idle);
> >
> > where __target_load and __source_load is where we take into account prio_bias.
We take that into consideration only while calculating the loads.. But we
don't scale it down while calculating imbalance, resulting in the problem
I mentioned.
> >
> > I'm not sure which code you're looking at, but Peter Williams is working on
> > rewriting the smp nice balancing code in -mm at the moment so that is quite
> > different from current linus tree.
> >
Peters changes in -mm fix this issue. Will this be pushed to Linus tree
before 2.6.16 comes out?
>
> Yes, indeed. And it would be very helpful if people interested in this
> topic (and that have test suites designed to test whether "niceness" is
> being well balanced across CPUs) could test it. This is especially the
> case for larger systems as I do not have ready access for testing on them.
I don't have any test suites for testing "niceness". But I can def check
more to make sure that it doesn't cause any regression :)
thanks,
suresh
>
> >
> >
> >>For example on a DP system with HT, if there are three runnable processes
> >>(simple infinite loop with same nice value), this patch is resulting in
> >>bouncing of these 3 processes from one processor to another...Lets assume
> >>if the 3 processes are scheduled as 2 in package-0 and 1 in package1..
> >>Now when the busy processor on package-1 does load balance and as
> >>imbalance doesn't take "prio_bias" into account, this will kick active
> >>load balance on package-0.. And this is continuing for ever, resulting
> >>in bouncing from one processor to another.
> >>
> >>Even when the system is completely loaded and if there is an imbalance,
> >>this patch causes wrong imabalance counts and cause unoptimized
> >>movements.
> >>
> >>Do you want to look into this and post a patch for 2.6.16?
next prev parent reply other threads:[~2006-01-26 23:56 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-26 10:52 smp 'nice' bias support breaks scheduler behavior Siddha, Suresh B
2006-01-26 12:25 ` Con Kolivas
2006-01-26 23:36 ` Peter Williams
2006-01-26 23:56 ` Siddha, Suresh B [this message]
2006-01-27 1:29 ` Con Kolivas
2006-01-27 1:34 ` Siddha, Suresh B
2006-01-27 1:54 ` Con Kolivas
2006-01-27 2:11 ` Siddha, Suresh B
2006-01-27 2:58 ` Con Kolivas
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