linux-kernel - Re: [PATCH v2 1/2] nvme: Add Arbitration Burst support

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Message-ID: <20200624075854.GA37292@VM20190228-100.tbsite.net>
Date:   Wed, 24 Jun 2020 15:58:54 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Christoph Hellwig <hch@....de>
Cc:     kbusch@...nel.org, axboe@...com, sagi@...mberg.me,
        baolin.wang7@...il.com, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] nvme: Add Arbitration Burst support

On Wed, Jun 24, 2020 at 08:52:58AM +0200, Christoph Hellwig wrote:
> On Wed, Jun 24, 2020 at 02:49:57PM +0800, Baolin Wang wrote:
> > >From the NVMe spec, "In order to make efficient use of the non-volatile
> > memory, it is often advantageous to execute multiple commands from a
> > Submission Queue in parallel. For Submission Queues that are using
> > weighted round robin with urgent priority class or round robin
> > arbitration, host software may configure an Arbitration Burst setting".
> > Thus add Arbitration Burst setting support.
> 
> What is the value add of doing this in the kernel?  Wouldn't a nvme-cli
> subcommand to just set the arbitration burst to the recommended value,
> either as a saved or current value be both more useful and also cause
> less kernel bloat?

Yes, that's another way to configure the RAB, but for some simple and
frequently-used usage cases, we just want to use the recommanded arbitration
burst as default without bothering the nvme-cli tool every reset time.