linux-kernel - Re: [patch] x64: Avoid irq_chip mask/unmask in fixup

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Date:	Thu, 04 Jun 2009 18:18:14 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"mingo@...e.hu" <mingo@...e.hu>, "hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"travis@....com" <travis@....com>,
	"steiner@....com" <steiner@....com>,
	Gary Hade <garyhade@...ibm.com>
Subject: Re: [patch] x64: Avoid irq_chip mask/unmask in fixup_irqs for
 interrupt-remapping

On Thu, 2009-06-04 at 16:13 -0700, Eric W. Biederman wrote:
> Suresh Siddha <suresh.b.siddha@...el.com> writes:
> 
> > From: Suresh Siddha <suresh.b.siddha@...el.com>
> > Subject: x64: Avoid irq_chip mask/unmask in fixup_irqs for interrupt-remapping
> >
> > In the presence of interrupt-remapping, irqs will be migrated in the
> > process context and we don't do (and there is no need to) irq_chip mask/unmask
> > while migrating the interrupt.
> >
> > Similarly fix the fixup_irqs() that get called during cpu offline and avoid
> > calling irq_chip mask/unmask for irqs that are ok to be migrated in the
> > process context.
> >
> > While we didn't observe any race condition with the existing code,
> > this change takes complete advantage of interrupt-remapping in
> > the newer generation platforms and avoids any potential HW lockup's
> > (that often worry Eric :)
> 
> You now apparently fail to migrate the irq threads in tandem with
> the rest of the irqs.

Eric, Are you referring to Gary's issues? As far as I understand, they
don't happen in the presence of interrupt-remapping.

Can you ack this patch, as this avoid touching IO-APIC and MSI entries
and does fixup_irqs() in a much more reliable fashion.

I haven't followed Gary's couple of patches related to non
interrupt-remapping case. I will go through them and see how I can help
there.

thanks,
suresh

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