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From: Jens Axboe <[email protected]>
To: Greg KH <[email protected]>, Phil Elwell <[email protected]>
Cc: [email protected], [email protected], [email protected],
	[email protected], [email protected],
	LKML <[email protected]>,
	[email protected], stable <[email protected]>
Subject: Re: [PATCH] io_uring: Use io_schedule* in cqring wait
Date: Mon, 24 Jul 2023 09:50:24 -0600	[thread overview]
Message-ID: <[email protected]> (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/[email protected]
> 
> 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


  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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