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

[Jens Axboe <axboe@kernel.dk>]

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 issue appears to have been introduced by a combination of two
> commits: 3bfe6106693b caused freeze on suspend-to-ram when mpd is paused
> or playing.  e4b4a13f4941 fixed suspend-to-ram, but introduced the high
> CPU on resume.
> 
> I attempted to further diagnose using `perf record -p $(pidof mpd)`.
> Running for about a minute after resume shows ~280 MMAP2 events and
> almost nothing else.  I'm not sure what to make of that or how to
> further investigate.
> 
> Let me know if there's anything else I can do to help diagnose/test.

Thanks for the report, let me take a look and try and reproduce (and
fix) it. I'll let you know if I fail in reproducing and need your
help in testing a fix!

-- 
Jens Axboe