linux-kernel - Re: [PATCH 1/2] sched_ext: Reimplement scx_bpf_reenqueue

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Message-ID: <20240709211847.GA248762@maniforge>
Date: Tue, 9 Jul 2024 16:18:47 -0500
From: David Vernet <void@...ifault.com>
To: Tejun Heo <tj@...nel.org>
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com,
	schatzberg.dan@...il.com
Subject: Re: [PATCH 1/2] sched_ext: Reimplement scx_bpf_reenqueue_local()

On Tue, Jul 09, 2024 at 11:09:42AM -1000, Tejun Heo wrote:
> scx_bpf_reenqueue_local() is used to re-enqueue tasks on the local DSQ from
> ops.cpu_release(). Because the BPF scheduler may dispatch tasks to the same
> local DSQ, to avoid processing the same tasks repeatedly, it first takes the
> number of queued tasks and processes the task at the head of the queue that
> number of times.
> 
> This is incorrect as a task can be dispatched to the same local DSQ with
> SCX_ENQ_HEAD. Such a task will be processed repeatedly until the count is
> exhausted and the succeeding tasks won't be processed at all.
> 
> Fix it by first moving all candidate tasks to a private list and then
> processing that list. While at it, remove the WARNs. They're rather
> superflous as later steps will check them anyway.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Fixes: 245254f7081d ("sched_ext: Implement sched_ext_ops.cpu_acquire/release()")
> Cc: David Vernet <void@...ifault.com>

Acked-by: David Vernet <void@...ifault.com>

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