linux-kernel - Re: [PATCH RFC] block, bfq: set default slice

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Date:   Thu, 1 Nov 2018 20:06:09 +0100
From:   Holger Hoffstätte <holger@...lied-asynchrony.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Paolo Valente <paolo.valente@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] block, bfq: set default slice_idle to zero for
 non-rotational devices

On 11/01/18 18:43, Konstantin Khlebnikov wrote:
> With default 8ms idle slice BFQ is up to 10 times slower than CFQ
> for massive random read workloads for common SATA SSD.
> 
> For now zero idle slice gives better out of box experience.
> CFQ employs this since commit 41c0126b3f22 ("block: Make CFQ default
> to IOPS mode on SSDs")

Well, that's interesting because 3 years ago I made the same suggestion
and was told that BFQ's heuristics automagically make it not idle when
rotational=0. Did you actually benchmark this? I just tried and don't
get a noticeable performance difference with slice_idle=0 compared to
deadline.

Discussion link:
https://groups.google.com/forum/#!msg/bfq-iosched/iRMw2n3kYLY/6l9cIm3TBgAJ

curious..

Holger