linux-kernel - Re: [RFC][PATCH] create workqueue threads only when needed

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Message-ID: <20090131182843.GD5884@nowhere>
Date:	Sat, 31 Jan 2009 19:28:45 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC][PATCH] create workqueue threads only when needed

On Sat, Jan 31, 2009 at 10:15:02AM -0800, Arjan van de Ven wrote:
> On Sat, 31 Jan 2009 19:03:49 +0100
> Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > > one thing to look at for work queues that never get work is to see
> > > if they are appropriate for the async function call interface
> > > (the only requirement for that is that they need to cope with
> > > calling inline in exceptional cases)
> > > 
> > 
> > 
> > Hi Arjan,
> > 
> > There is one thing that make it hard to replace workqueues in such
> > cases, there is not guarantee the function will run in user context
> > because of this condition:
> > 
> > if (!async_enabled || !entry || atomic_read(&entry_count) > MAX_WORK)
> > 
> > I wanted to replace kpsmoused with an async function but I want to
> > schedule a slow work that can't be done from irq...
> 
> if there is enough value in having a variant that is guaranteed to
> always run from a thread we could add that. Likely that needs that the 
> caller passes in a bit of memory, but that's not too big a deal.
> If there is only 1 in the entire kernel it might not be worth it,
> but if it's a common pattern then for sure...
> 
> do you have a feeling on how common this is ?
> 


I don't know, most of those I've looked on are not documented about the reason
for a private workqueue. I guess most of them can use the usual kevent.

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