linux-kernel - Re: [patch 11/26] x64, x2apic/intr-remap: generic irq migration support from process context

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Date:	Thu, 10 Jul 2008 22:41:06 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"mingo@...e.hu" <mingo@...e.hu>, "hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"steiner@....com" <steiner@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [patch 11/26] x64, x2apic/intr-remap: generic irq migration support from process context

On Thu, Jul 10, 2008 at 04:08:03PM -0700, Eric W. Biederman wrote:
> Suresh Siddha <suresh.b.siddha@...el.com> writes:
> 
> > Generic infrastructure for migrating the irq from the process context in the
> > presence of CONFIG_GENERIC_PENDING_IRQ.
> >
> > This will be used later for migrating irq in the presence of
> > interrupt-remapping.
> 
> Why the API difference between IRQ_MOVE_PCNTXT set affinity handlers and
> !CONFIG_GENERIC_PENDING_IRQ handlers?

You are referring to desc->lock portion?

Two reasons:

a. Other code in CONFIG_GENERIC_PENDING_IRQ, assuming that desc->lock is held
while calling set_affinity. like fixup_irqs(). Just wanted to be same
across the board.

b. for level triggered, we still touch irq_desc and set IRQ_MOVE_PENDING,
when we fail to move the irq (if there is already some level triggered
interrupt happening in parallel). while, we can acquire the lock inside
the set_affinity, I thought this simplifies things.

> 
> 
> >  #ifdef CONFIG_GENERIC_PENDING_IRQ
> > -     set_pending_irq(irq, cpumask);
> > +     if (desc->status & IRQ_MOVE_PCNTXT) {
> > +             unsigned long flags;
> > +
> > +             spin_lock_irqsave(&desc->lock, flags);
> > +             desc->chip->set_affinity(irq, cpumask);
> > +             spin_unlock_irqrestore(&desc->lock, flags);
> > +     } else
> > +             set_pending_irq(irq, cpumask);
> >  #else
> >       desc->affinity = cpumask;
> >       desc->chip->set_affinity(irq, cpumask);
> >
> > --

thanks,
suresh
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