linux-kernel - Re: [PATCH 9/9] workqueue: Implement system-wide nr_active enforcement for unbound workqueues

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Date: Wed, 24 Jan 2024 10:54:26 +0800
From: Lai Jiangshan <jiangshanlai@...il.com>
To: Tejun Heo <tj@...nel.org>
Cc: linux-kernel@...r.kernel.org, Naohiro.Aota@....com, kernel-team@...a.com
Subject: Re: [PATCH 9/9] workqueue: Implement system-wide nr_active
 enforcement for unbound workqueues

Hello, Tejun

On Wed, Jan 24, 2024 at 8:30 AM Tejun Heo <tj@...nel.org> wrote:

> > >  /**
> > >   * pwq_activate_first_inactive - Activate the first inactive work item on a pwq
> > >   * @pwq: pool_workqueue of interest
> > > + * @fill: max_active may have increased, try to increase concurrency level
> >
> > I think it is also legitimate to increase the concurrency level ASAP
> > when called from try_to_grab_pending() path.
>
> Can you elaborate why that'd be useful?
>

If an active item for a PWQ is canceled, the PWQ will lose a hard-earned
nr_active and have to wait on the round-robbin queue for another nr_active.

It seems it is unfair for this PWQ. If a user's program pattern is
queuing-checking-cancelling items, it can cause delays for other users
sharing the same workqueue.

Thanks
Lai