linux-kernel - Re: [RFC] sched_tick with interrupts enabled

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Date:	Thu, 19 Oct 2006 19:16:23 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc:	clameter@....com, nickpiggin@...oo.com.au,
	suresh.b.siddha@...el.com, mingo@...e.hu, pwil3058@...pond.net.au,
	linux-kernel@...r.kernel.org,
	"kaneshige.kenji@...t.fujitsu.com" <kaneshige.kenji@...t.fujitsu.com>
Subject: Re: [RFC] sched_tick with interrupts enabled

On Wed, 18 Oct 2006 19:19:00 -0700
"Siddha, Suresh B" <suresh.b.siddha@...el.com> wrote:

> On Wed, Oct 18, 2006 at 02:59:07PM -0700, Christoph Lameter wrote:
> > load_balancing has the potential of running for some time if f.e.
> > sched_domains for a system with 1024 processors have to be balanced.
> > We currently do all of that with interrupts disabled. So we may be unable
> > to service interrupts for some time. Most of that time is potentially
> > spend in rebalance_tick.
> 
> Did you see an issue because of this or just theoretical?
> 

IIRC, Fujitsu's 64-cpu ia64/SMP system sufferred from this issue *in older kernel*. 
Now, we avoid it by creating NUMA nodes and dividing scheduler domains.

Situation was...:
5 runnable processes which were pinned to a cpu in a 64cpu system.
the system was always rebalanced and seems to be hanged.

-Kame

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