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

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Date:   Mon, 29 Oct 2018 13:25:30 -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 14:09 -0600, Jens Axboe wrote:
> hctx->type will be set to the value of the first type. This is all driver
> private, blk-mq could not care less what the value of the type means.
> 
> As to the other question, it works just fine since that is the queue
> that is being accessed. There's no confusion there. I think you're
> misunderstanding how it's seutp. To use nvme as the example, type 0
> would be reads, 1 writes, and 2 pollable queues. If reads and writes
> share the same set of hardware queues, then type 1 simply doesn't
> exist in terms of ->flags_to_type() return value. This is purely
> driven by the driver. That hook is the only decider of where something
> will go. If we share hctx sets, we share the same hardware queue as
> well. There is just the one set for that case.

How about adding a comment in blk-mq.h that explains that hardware queues can
be shared among different hardware queue types? I think this is nontrivial and
deserves a comment.

Thanks,

Bart.