linux-kernel - Re: [PATCH 10/14] blk-mq: initial support for multiple queue maps

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Date:   Mon, 29 Oct 2018 12:40:34 -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 10/14] blk-mq: initial support for multiple queue maps

On Mon, 2018-10-29 at 10:37 -0600, Jens Axboe wrote:
> -static int cpu_to_queue_index(unsigned int nr_queues, const int cpu)
> +static int cpu_to_queue_index(struct blk_mq_queue_map *qmap,
> +			      unsigned int nr_queues, const int cpu)
>  {
> -	return cpu % nr_queues;
> +	return qmap->queue_offset + (cpu % nr_queues);
>  }
> 
> [ ... ]
>  
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -78,10 +78,11 @@ struct blk_mq_hw_ctx {
>  struct blk_mq_queue_map {
>  	unsigned int *mq_map;
>  	unsigned int nr_queues;
> +	unsigned int queue_offset;
>  };

I think it's unfortunate that the blk-mq core uses the .queue_offset member but
that mapping functions in block drivers are responsible for setting that member.
Since the block driver mapping functions have to set blk_mq_queue_map.nr_queues,
how about adding a loop in blk_mq_update_queue_map() that derives .queue_offset
from .nr_queues from previous array entries?

Thanks,

Bart.