linux-kernel - Re: MQ-BFQ crashing on battery mode

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Date:   Fri, 24 Aug 2018 08:29:16 +0200
From:   Massimo Burcheri <massimo@...cheri.de>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Omar Sandoval <osandov@...ndov.com>
Subject: Re: MQ-BFQ crashing on battery mode

On Wed, 2018-08-22 at 11:42 -0600, Jens Axboe wrote:
> Any chance you can try 4.18 at least?

Of course, I tried the kernel.org sources now, sys-kernel/vanilla-sources-4.18.3 
on Gentoo. The issue is the same.

I wonder that nobody has noticed that issue that I can reproduce on many kernels
since 4.13 or even older. Is it a rare combination with my bcache, luks or
btrfs? Or hardware specific? Or scheduler specific, as even BFQ is not that well
tested on btrfs like the default one.

> Schedulers are specific to the queuing infrastructure, so certain types
> will only be available with MQ and certain types will only be available
> on !MQ.

I noticed that. It's just a bit intransparent from the menuconfig, options don't
mention if a scheduler is working on MQ or not, like CONFIG_IOSCHED_BFQ.
There it's written in the description, while CONFIG_MQ_IOSCHED_KYBER has the
note in the name.
Actually MQ schedulers could depend on BLK_MQ to make it obvious.

Best regards,
Massimo
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