linux-kernel - Re: [PATCH 11/13] blk-mq: allow the driver to pass in an affinity mask

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Message-ID: <20160710034144.GA15720@lst.de>
Date:	Sun, 10 Jul 2016 05:41:44 +0200
From:	Christoph Hellwig <hch@....de>
To:	Alexander Gordeev <agordeev@...hat.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: [PATCH 11/13] blk-mq: allow the driver to pass in an affinity
	mask

On Mon, Jul 04, 2016 at 11:35:28AM +0200, Alexander Gordeev wrote:
> > mq_map is initialized to zero already, so we don't really need the
> > assignment for queue 0.  The reason why this check exists is because
> > we start with queue = -1 and we never want to assignment -1 to mq_map.
> 
> Would this read better then?
> 
> 	int queue = 0;
> 
> 	...
> 
> 	/* If cpus are offline, map them to first hctx */
> 	for_each_online_cpu(cpu) {
> 		set->mq_map[cpu] = queue;
> 		if (cpumask_test_cpu(cpu, affinity_mask))
> 			queue++;

It would read better, but I don't think it's actually correct.
We'd still assign the 'old' queue to the cpu that is set in the affinity
mask.