linux-kernel - Re: [patch 1/2] sched: fix idle load balancing in softirqd context

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Date:	Sat, 17 Feb 2007 09:42:16 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
cc:	mingo@...e.hu, linux-kernel@...r.kernel.org, npiggin@...e.de
Subject: Re: [patch 1/2] sched: fix idle load balancing in softirqd context



On Fri, 16 Feb 2007, Siddha, Suresh B wrote:

> Periodic load balancing in recent kernels happen in the softirq.
> In certain -rt configurations, these softirqs are handled in softirqd
> context. And hence the check for idle processor was always returning
> busy (as nr_running > 1).
>
> This patch captures the idle information at the tick and passes this info
> to softirq context through an element 'idle_at_tick' in rq.

I haven't had the time yet to look too detailed at this patch.

>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
>

>  {
>  	unsigned long long now = sched_clock();
>  	struct task_struct *p = current;
> -	int cpu = smp_processor_id();
> +	int cpu = smp_processor_id(), idle_at_tick = idle_cpu(cpu);
>  	struct rq *rq = cpu_rq(cpu);
>

But I would recommend that the idle_at_tick should be on a separate line.

I'll try to look deeper at your patches tomorrow. I've also found that I'm
having some latency problems in -rt that I think might be related to
migration.

-- Steve

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