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

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Date:	Thu, 16 Jun 2016 17:16:13 +0200
From:	Christoph Hellwig <hch@....de>
To:	"Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>
Cc:	Christoph Hellwig <hch@....de>, linux-block@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-nvme@...ts.infradead.org, axboe@...com, tglx@...utronix.de,
	bart.vanassche@...disk.com
Subject: Re: [PATCH 06/13] irq: add a helper spread an affinity mask for
	MSI/MSI-X vectors

>
> ...but now I'll focus on the common/general case! Thanks for the suggestion 
> Christoph. I guess would be even better to have a generic function that 
> retrieves an optimal mask, something like topology_get_optimal_mask(n, 
> *cpumask), in which we get the best distribution of n CPUs among all cores 
> and return such a mask - interesting case is when n < num_online_cpus. So, 
> this function could be used inside your irq_create_affinity_mask() and 
> maybe in other places it is needed.

Yes, we should probably just plug this in where we're using the current
routines.  Block very much optimizes for the cases of either 1 queue
or enough queues for all cpus at the moments.  It would be good to check
what the network drivers currently do.