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

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Date:	Tue, 21 Jun 2016 16:31:20 +0200
From:	Christoph Hellwig <hch@....de>
To:	Bart Van Assche <bart.vanassche@...disk.com>
Cc:	Christoph Hellwig <hch@....de>,
	Keith Busch <keith.busch@...el.com>,
	"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 Mon, Jun 20, 2016 at 03:21:47PM +0200, Bart Van Assche wrote:
> A notification mechanism that reports interrupt mapping changes will 
> definitely help. What would also help is an API that allows drivers to 
> query the MSI-X IRQ of an adapter that is nearest given a cpumask, e.g. 
> hctx->cpumask.

This is still the wrong way around - we need to build the blk-mq queue
mappings based on the interrupts, not the other way around.

> Another function can then map that IRQ into an index in the 
> range 0..n-1 where n is the number of MSI-X interrupts for that adapter. 
> Every blk-mq/scsi-mq driver will need this functionality to decide which 
> IRQ to associate with a block layer hctx.

This is something that should be done in commmon code and is done in
common code in this series - the driver passes a cpumask to blk-mq,
and blk-mq creates a queue for every cpu that is set in the cpumask.