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

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Date:	Tue, 20 Feb 2007 22:25:09 -0800
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>, 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 Sat, Feb 17, 2007 at 09:42:16AM -0500, Steven Rostedt wrote:
> On Fri, 16 Feb 2007, Siddha, Suresh B wrote:
> > -	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.

Ok.

> 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.

There is one more issue, I have observed in -rt tree.

raise_softirq_irqoff() is unconditionally doing the wakeup_softirqd()
But unless the CONFIG_PREEMPT_SOFTIRQS is configured, do_softirq()
will process the softirq's like TIMER_SOFTIRQ and SCHED_SOFTIRQ in the
process context.  So it looks like we are unnecessarily waking the
softirqd's corresponding to those softirq's.

thanks,
suresh
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