linux-kernel - Re: [PATCH 2/2] sched_ext: Make scx_bpf_reenqueue_local() skip tasks that are being migrated

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Message-ID: <20240709221648.GB248762@maniforge>
Date: Tue, 9 Jul 2024 17:16:48 -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 2/2] sched_ext: Make scx_bpf_reenqueue_local() skip tasks
 that are being migrated

On Tue, Jul 09, 2024 at 11:09:43AM -1000, Tejun Heo wrote:
> When a running task is migrated to another CPU, the stop_task is used to
> preempt the running task and migrate it. This, expectedly, invokes
> ops.cpu_release(). If the BPF scheduler then calls
> scx_bpf_reenqueue_local(), it re-enqueues all tasks on the local DSQ
> including the task which is being migrated.
> 
> This creates an unnecessary re-enqueue of a task which is about to be
> deactivated and re-activated for migration anyway. It can also cause
> confusion for the BPF scheduler as scx_bpf_task_cpu() of the task and its
> allowed CPUs may not agree while migration is pending.
> 
> 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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