linux-kernel - Re: automatic interrupt affinity for MSI/MSI-X capable devices V2

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Date:	Thu, 16 Jun 2016 17:22:37 +0200
From:	Christoph Hellwig <hch@....de>
To:	Bart Van Assche <bart.vanassche@...disk.com>
Cc:	Christoph Hellwig <hch@....de>, 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: automatic interrupt affinity for MSI/MSI-X capable devices V2

On Thu, Jun 16, 2016 at 11:45:55AM +0200, Bart Van Assche wrote:
> Is my interpretation correct that for an adapter that supports two 
> interrupts and on a system with eight CPU cores and no hyperthreading this 
> patch series will assign interrupt vector 0 to CPU 0 and interrupt vector 1 
> to CPU 1?

Yes - same as the existing blk-mq queue distribution.

> Are you aware that drivers like ib_srp assume that interrupts 
> have been spread evenly, that means assigning vector 0 to CPU 0 and vector 
> 1 to CPU 4?

which will make them run into a conflict with the current blk-mq
assignment.  That's exactly the point why we're trying to move things
to a core location so that everyone can use the same mapping.