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

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Message-ID: <4985CC57.7090800@s5r6.in-berlin.de>
Date:	Sun, 01 Feb 2009 17:22:47 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Arjan van de Ven <arjan@...radead.org>,
	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

Frederic Weisbecker wrote:
> 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:
>>> 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.

I have stuff in drivers/firewire/ done in a private workqueue and some
in the shared workqueue which I will eventually move either into
short-lived ad hoc created kthreads /or/ preferably into a thread pool
implementation --- if such a thing will have found its way into the
kernel when I have time for my project.

I need to get callers of scsi_add_device and scsi_remove_device out of
the picture.
-- 
Stefan Richter
-=====-==--= --=- ----=
http://arcgraph.de/sr/
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