linux-kernel - Re: [patch] sched: fix newly idle load balance in case of SMT

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Message-ID: <20070717081542.GB17234@elte.hu>
Date:	Tue, 17 Jul 2007 10:15:42 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc:	npiggin@...e.de, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [patch] sched: fix newly idle load balance in case of SMT


* Siddha, Suresh B <suresh.b.siddha@...el.com> wrote:

> In the presence of SMT, newly idle balance was never happening for 
> multi-core and SMP domains(even when both the logical siblings are 
> idle).
> 
> If thread 0 is already idle and when thread 1 is about to go to idle, 
> newly idle load balance always think that one of the threads is not 
> idle and skips doing the newly idle load balance for multi-core and 
> SMP domains.
> 
> This is because of the idle_cpu() macro, which checks if the current 
> process on a cpu is an idle process. But this is not the case for the 
> thread doing the load_balance_newidle().
> 
> Fix this by using runqueue's nr_running field instead of idle_cpu(). 
> And also skip the logic of 'only one idle cpu in the group will be 
> doing load balancing' during newly idle case.

ah, indeed - good catch! I've checked the other uses of idle_cpu() and 
those seem to be fine. I've added your patch to my queue.

	Ingo
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