linux-kernel - Re: [v5.12-rc2 regression] io_uring: high CPU use after suspend-to-ram

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Message-ID: <344c1326-0d32-c855-4c30-cfefd9746a2a@kernel.dk>
Date:   Wed, 10 Mar 2021 07:45:03 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Kevin Locke <kevin@...inlocke.name>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, rafael.j.wysocki@...el.com
Subject: Re: [v5.12-rc2 regression] io_uring: high CPU use after
 suspend-to-ram

On 3/9/21 8:23 PM, Kevin Locke wrote:
> On Tue, 2021-03-09 at 19:48 -0700, Jens Axboe wrote:
>> On 3/9/21 6:55 PM, Kevin Locke wrote:
>>> With kernel 5.12-rc2 (and torvalds/master 144c79ef3353), if mpd is
>>> playing or paused when my system is suspended-to-ram, when the system is
>>> resumed mpd will consume ~200% CPU until killed.  It continues to
>>> produce audio and respond to pause/play commands, which do not affect
>>> CPU usage.  This occurs with either pulse (to PulseAudio or
>>> PipeWire-as-PulseAudio) or alsa audio_output.
>>
>> The below makes it work as expected for me - but I don't quite
>> understand why we're continually running after the freeze. Adding Rafael
>> to help understand this.
> 
> I can confirm that your patch resolves the high CPU usage after suspend
> on my system as well.  Many thanks!
> 
> Tested-by: Kevin Locke <kevin@...inlocke.name>
> 
> Happy to test any future revisions as well.

Thanks, I'll just hold on to this version for now. It's how it would've
worked before the thread rework anyway. I'd still like to understand why
the thaw leaves them spinning, though :-). But once that is understood,
we can potentially just enable freezing again as a separate patch.
Fixing this one is more important for the time being.

-- 
Jens Axboe