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

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Message-ID: <20160704081540.GA2783@agordeev.lab.eng.brq.redhat.com>
Date:	Mon, 4 Jul 2016 10:15:41 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Christoph Hellwig <hch@....de>
Cc:	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 Tue, Jun 14, 2016 at 09:59:04PM +0200, Christoph Hellwig wrote:
> +static int blk_mq_create_mq_map(struct blk_mq_tag_set *set,
> +		const struct cpumask *affinity_mask)
> +{
> +	int queue = -1, cpu = 0;
> +
> +	set->mq_map = kzalloc_node(sizeof(*set->mq_map) * nr_cpu_ids,
> +			GFP_KERNEL, set->numa_node);
> +	if (!set->mq_map)
> +		return -ENOMEM;
> +
> +	if (!affinity_mask)
> +		return 0;	/* map all cpus to queue 0 */
> +
> +	/* If cpus are offline, map them to first hctx */
> +	for_each_online_cpu(cpu) {
> +		if (cpumask_test_cpu(cpu, affinity_mask))
> +			queue++;

CPUs missing in an affinity mask are mapped to hctxs. Is that intended?

> +		if (queue > 0)

Why this check?

> +			set->mq_map[cpu] = queue;
> +	}
> +
> +	return 0;
> +}
> +