linux-kernel - Re: [PATCH 02/13] irq: Introduce IRQD_AFFINITY

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Date:	Wed, 15 Jun 2016 17:28:54 +0200
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Keith Busch <keith.busch@...el.com>
CC:	Christoph Hellwig <hch@....de>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"axboe@...com" <axboe@...com>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 02/13] irq: Introduce IRQD_AFFINITY_MANAGED flag

On 06/15/2016 05:14 PM, Keith Busch wrote:
> On Wed, Jun 15, 2016 at 12:42:53PM +0200, Bart Van Assche wrote:
>> If two identical adapters are present in a system, will these generate the
>> same irq_affinity mask? Do you agree that interrupt vectors from different
>> adapters should be assigned to different CPU cores if enough CPU cores are
>> available? If so, which software layer will assign interrupt vectors from
>> different adapters to different CPU cores?
>
> I think the idea is have the irq_affinity mask match the CPU mapping on
> the submission side context associated with that particular vector. If
> two identical adapters generate the same submission CPU mapping, I don't
> think we can do better than matching irq_affinity masks.

Has this been verified by measurements? Sorry but I'm not convinced that 
using the same mapping for multiple identical adapters instead of 
spreading interrupts will result in better performance.

Bart.