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From: Phil Elwell <phil@raspberrypi.com>
To: axboe@kernel.dk
Cc: andres@anarazel.de, asml.silence@gmail.com, david@fromorbit.com,
	hch@lst.de, io-uring@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	linux-xfs@vger.kernel.org, stable <stable@vger.kernel.org>
Subject: Re: [PATCH] io_uring: Use io_schedule* in cqring wait
Date: Mon, 24 Jul 2023 16:35:43 +0100	[thread overview]
Message-ID: <CAMEGJJ2RxopfNQ7GNLhr7X9=bHXKo+G5OOe0LUq=+UgLXsv1Xg@mail.gmail.com> (raw)

Hi Andres,

With this commit applied to the 6.1 and later kernels (others not
tested) the iowait time ("wa" field in top) in an ARM64 build running
on a 4 core CPU (a Raspberry Pi 4 B) increases to 25%, as if one core
is permanently blocked on I/O. The change can be observed after
installing mariadb-server (no configuration or use is required). After
reverting just this commit, "wa" drops to zero again.

I can believe that this change hasn't negatively affected performance,
but the result is misleading. I also think it's pushing the boundaries
of what a back-port to stable should do.

Phil

             reply	other threads:[~2023-07-24 15:35 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-24 15:35 Phil Elwell [this message]
2023-07-24 15:48 ` [PATCH] io_uring: Use io_schedule* in cqring wait Greg KH
2023-07-24 15:50   ` Jens Axboe
2023-07-24 15:58     ` Jens Axboe
2023-07-24 16:07       ` Phil Elwell
2023-07-24 16:08         ` Jens Axboe
2023-07-24 16:48           ` Phil Elwell
2023-07-24 18:22             ` Jens Axboe
2023-07-24 19:22       ` Pavel Begunkov
2023-07-24 20:27         ` Jeff Moyer
2023-07-24 15:48 ` Jens Axboe
2023-07-24 16:16   ` Andres Freund
2023-07-24 16:20     ` Jens Axboe
2023-07-24 17:24     ` Andres Freund
2023-07-24 17:44       ` Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2023-07-18 19:49 [PATCHSET v2 0/5] Improve async iomap DIO performance Jens Axboe
2023-07-18 19:49 ` [PATCH] io_uring: Use io_schedule* in cqring wait Jens Axboe
2023-07-18 19:50   ` Jens Axboe

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