From: Jens Axboe <axboe@kernel.dk>
To: Greg KH <gregkh@linuxfoundation.org>, Phil Elwell <phil@raspberrypi.com>
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 09:50:24 -0600 [thread overview]
Message-ID: <140065e3-0368-0b5d-8a0d-afe49b741ad2@kernel.dk> (raw)
In-Reply-To: <2023072438-aftermath-fracture-3dff@gregkh>
On 7/24/23 9:48?AM, Greg KH wrote:
> On Mon, Jul 24, 2023 at 04:35:43PM +0100, Phil Elwell wrote:
>> 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.
>
> This has been discussed already:
> https://lore.kernel.org/r/12251678.O9o76ZdvQC@natalenko.name
>
> It's not a bug, mariadb does have pending I/O, so the report is correct,
> but the CPU isn't blocked at all.
Indeed - only thing I can think of is perhaps mariadb is having a
separate thread waiting on the ring in perpetuity, regardless of whether
or not it currently has IO.
But yes, this is very much ado about nothing...
--
Jens Axboe
next prev parent reply other threads:[~2023-07-24 15:50 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-24 15:35 [PATCH] io_uring: Use io_schedule* in cqring wait Phil Elwell
2023-07-24 15:48 ` Greg KH
2023-07-24 15:50 ` Jens Axboe [this message]
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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