linux-kernel - Re: [PATCH] nvme: Acknowledge completion queue on each iteration

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Date:   Mon, 17 Jul 2017 18:45:51 -0400
From:   Keith Busch <keith.busch@...el.com>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     linux-nvme@...ts.infradead.org, timur@...eaurora.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: Acknowledge completion queue on each iteration

On Mon, Jul 17, 2017 at 06:36:23PM -0400, Sinan Kaya wrote:
> Code is moving the completion queue doorbell after processing all completed
> events and sending callbacks to the block layer on each iteration.
> 
> This is causing a performance drop when a lot of jobs are queued towards
> the HW. Move the completion queue doorbell on each loop instead and allow new
> jobs to be queued by the HW.

That doesn't make sense. Aggregating doorbell writes should be much more
efficient for high depth workloads.