linux-kernel - Re: [PATCH RFC] irq: Set CPU affinity as soon as the irq thread is created

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Date:	Tue, 9 Oct 2012 22:25:36 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Sankara Muthukrishnan <sankara.m@...il.com>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] irq: Set CPU affinity as soon as the irq thread is
 created

On Wed, 5 Sep 2012, Steven Rostedt wrote:

> On Wed, 2012-09-05 at 18:07 -0500, Sankara Muthukrishnan wrote:
> > Hi there,
> 
> This also affects mainline. Please Cc LKML (as I did).
> 
> > 
> > As irq_thread_check_affinity is called inside the while loop in the
> > IRQ thread, the core affinity is set only when an interrupt happens.
> > It does not seem to be a bad idea to set the core affinity soon after
> > the thread is created also (as shown in the patch).
> > irq_thread_check_affinity calls kmalloc_node that can sleep.
> 
> Note, it only calls kmalloc if you enable CONFIG_CPUMASK_OFFSTACK, which
> you probably don't on an embedded device. But you might. Your embedded
> device may have more than 32 or 64 CPUs.
> 
> I'd be more worried about calling set_cpus_allowed_ptr() than kmalloc().
> 
> >  In an
> > embedded target where IRQ affinities are pre-configured during
> > boot-time (and not modified through /proc/irq/../smp_affinity) during
> > run-time, the extra latency due to irq_thread_check_affinity can be
> > avoided during processing of the first interrupt with this patch.
> > Thoughts?

Yes, this needs a proper Signed-off-by and an update against current
mainline.

Thanks,

	tglx

> > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> > index 87dc053..bf2cdc2 100644
> > --- a/kernel/irq/manage.c
> > +++ b/kernel/irq/manage.c
> > @@ -791,6 +791,7 @@ static int irq_thread(void *data)
> > 
> >         sched_setscheduler(current, SCHED_FIFO, &param);
> >         current->irqaction = action;
> > +       irq_thread_check_affinity(desc, action);
> > 
> >         while (!irq_wait_for_interrupt(action)) {
> 
> I see no problem with this patch.
> 
> Acked-by: Steven Rostedt <rostedt@...dmis.org>
> 
> -- Steve
> 
> 
> --
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