linux-kernel - Re: [PATCH 08/14] blk-mq: separate number of hardware queues from nr_cpu

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Date:   Mon, 29 Oct 2018 11:31:16 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/14] blk-mq: separate number of hardware queues from
 nr_cpu_ids

On Mon, 2018-10-29 at 10:37 -0600, Jens Axboe wrote:
> With multiple maps, nr_cpu_ids is no longer the maximum number of
> hardware queues we support on a given devices. The initializer of
> the tag_set can have set ->nr_hw_queues larger than the available
> number of CPUs, since we can exceed that with multiple queue maps.
> 
> Reviewed-by: Hannes Reinecke <hare@...e.com>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> ---
>  block/blk-mq.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 0fab36372ace..60a951c4934c 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2663,6 +2663,19 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
>  	mutex_unlock(&q->sysfs_lock);
>  }
>  
> +/*
> + * Maximum number of queues we support. For single sets, we'll never have
                       ^
                   hardware?
> + * more than the CPUs (software queues). For multiple sets, the tag_set
> + * user may have set ->nr_hw_queues larger.
> + */

Anyway:

Reviewed-by: Bart Van Assche <bvanassche@....org>