linux-kernel - Re: [PATCH] genirq: fix symbol export for __irq_set

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Message-ID: <alpine.DEB.2.11.1412190004530.17382@nanos>
Date:	Fri, 19 Dec 2014 00:11:52 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jesse Brandeburg <jesse.brandeburg@...el.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] genirq: fix symbol export for __irq_set_affinity

On Thu, 18 Dec 2014, Jesse Brandeburg wrote:
> On Thu, 18 Dec 2014 23:42:03 +0100
> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > On Thu, 18 Dec 2014, Jesse Brandeburg wrote:
> > > Enabling this function means that kernel drivers can include
> > > an initial affinity setting for the interrupt, instead of all
> > > interrupts starting out life on CPU0.  It seems to have just
> > > been an oversight that it was not included.
> 
> > And why needs this to be called from modules? Just because or is there
> > a legitimate reason? IOW, you forgot to describe the actual usecase.
> 
> As stated above, the use case for my interest is making a network
> driver's many interrupt vectors not all show up on CPU0.  Of course a
> user can work around this by manually tuning smp_affinity, but I have
> seen many reports from users and testers where the performance of the
> network was really bad due to all network interrupts on CPU0.
> 
> This allows the driver to set a sane default smp_affinity value at
> driver load.

Fair enough. Overloaded brain missed parts of the explanation. :)
 
> Would you instead consider a patch where if a user calls the
> set_irq_affinity_hint that the initial affinity is set to the hinted
> value?

That would make a lot of sense, because you probably will set the
affinity hint anyway, right?

Thanks,

	tglx



 
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