linux-kernel - Re: [PATCH V2] Consider inflight IO in io accounting for high latency devices

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Message-ID: <d10c329b-85c9-4bc2-be00-f156c48639e5@acm.org>
Date:   Mon, 16 Oct 2023 14:16:09 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Gulam Mohamed <gulam.mohamed@...cle.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] Consider inflight IO in io accounting for high latency
 devices

On 10/16/23 13:01, Gulam Mohamed wrote:
> [GULAM]: Yes, it will be called for every submitted bio but for the
> high latency devices it will not have much impact. This is indicated
> by the latency figures I provided in the review mail, with and
> without our patch.

Calling tag iteration code from the hot path is wrong.

There are more devices than only hard disks that have a single hardware
queue, e.g. certain SSDs. I'm pretty sure that this patch will have a
significant negative performance impact for such devices.

Thanks,

Bart.