linux-kernel - Re: [PATCH 1/2] sched/core: switch struct rq->nr

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Date: Thu, 29 Feb 2024 17:53:40 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, mingo@...hat.com, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 1/2] sched/core: switch struct rq->nr_iowait to a normal
 int

On Wed, Feb 28 2024 at 12:16, Jens Axboe wrote:
> In 3 of the 4 spots where we modify rq->nr_iowait we already hold the

We modify something and hold locks? It's documented that changelogs
should not impersonate code. It simply does not make any sense.

> rq lock, and hence don't need atomics to modify the current per-rq
> iowait count. In the 4th case, where we are scheduling in on a different
> CPU than the task was previously on, we do not hold the previous rq lock,
> and hence still need to use an atomic to increment the iowait count.
>
> Rename the existing nr_iowait to nr_iowait_remote, and use that for the
> 4th case. The other three cases can simply inc/dec in a non-atomic
> fashion under the held rq lock.
>
> The per-rq iowait now becomes the difference between the two, the local
> count minus the remote count.
>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>

Other than that:

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>