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

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Message-ID: <20170718212631.GB1202@localhost.localdomain>
Date:   Tue, 18 Jul 2017 17:26:32 -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 Tue, Jul 18, 2017 at 02:52:26PM -0400, Sinan Kaya wrote:
> On 7/18/2017 10:36 AM, Keith Busch wrote:
> 
> I do see that the NVMe driver is creating a completion interrupt on
> each CPU core for the completions. No problems with that. 
> 
> However, I don't think you can guarantee that there will always be a single
> CPU core targeting one submission queue especially with asynchronous IO.
>
> Lock contention counters from CONFIG_LOCK_STAT are pointing to nvmeq->lock
> in my FIO tests.
> 
> Did I miss something?

I think that must mean your machine has many more CPUs than your nvme
controller has IO queues.