linux-kernel - Re: [PATCH 06/13] irq: add a helper spread an affinity mask for MSI/MSI-X vectors

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Date:	Fri, 1 Jul 2016 09:25:27 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Christoph Hellwig <hch@....de>
Cc:	tglx@...utronix.de, axboe@...com, linux-block@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/13] irq: add a helper spread an affinity mask for
 MSI/MSI-X vectors

On Thu, Jun 30, 2016 at 07:48:54PM +0200, Christoph Hellwig wrote:
> On Sat, Jun 25, 2016 at 10:05:19PM +0200, Alexander Gordeev wrote:
> > > + * and generate an output cpumask suitable for spreading MSI/MSI-X vectors
> > > + * so that they are distributed as good as possible around the CPUs.  If
> > > + * more vectors than CPUs are available we'll map one to each CPU,
> > 
> > Unless I do not misinterpret a loop from msix_setup_entries() (patch 08/13),
> > the above is incorrect:
> 
> What part do you think is incorrect?

With your explanations below and no immediate intention to fix the
algorithm it is correct.

> > (*) I guess, in some topology configurations a total number of all
> > first siblings may be less than the number of vectors.
> 
> Yes, in that case we'll assign imcompetely.  I've already heard people
> complaining about that at LSF/MM, but no one volunteered patches.
> I only have devices with 1 or enough vectores to test, so I don't
> really dare to touch the algorithm.  Either way the algorithm
> change should probably be a different patch than refactoring it and
> moving it around.

I see your approach now. Thanks!