Date: Thu, 18 Dec 2014 14:48:36 -0800
From: Jesse Brandeburg <jesse.brandeburg@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] genirq: fix symbol export for __irq_set_affinity
Message-ID: <20141218144836.0000091d@unknown>
In-Reply-To: <alpine.DEB.2.11.1412182340300.17382@nanos>
References: <20141218223031.23847.86103.stgit@jbrandeb-cp2.jf.intel.com>
	<alpine.DEB.2.11.1412182340300.17382@nanos>
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Sender: linux-kernel-owner@vger.kernel.org

On Thu, 18 Dec 2014 23:42:03 +0100
Thomas Gleixner <tglx@linutronix.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.

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?
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