linux-kernel - Re: [PATCH 1/2] workqueues: implement flush

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Message-ID: <20080614091339.GA2466@ami.dom.local>
Date:	Sat, 14 Jun 2008 11:13:40 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jarek Poplawski <jarkao2@...pl>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] workqueues: implement flush_work()

On Fri, Jun 13, 2008 at 06:28:01PM +0400, Oleg Nesterov wrote:
> (on top of [PATCH] workqueues: insert_work: use "list_head *" instead of "int tail"
>  http://marc.info/?l=linux-kernel&m=121328944230175)
> 
> Most of users of flush_workqueue() can be changed to use cancel_work_sync(),
> but sometimes we really need to wait for the completion and cancelling is not
> an option. schedule_on_each_cpu() is good example.
> 
> Add the new helper, flush_work(work), which waits for the completion of the
> specific work_struct.

This all looks right and better than current flush_, but... the main
problem is that probably in 90% cases cancel_ + self-running a work
function (if cancelled) should be both more efficient and safer wrt
locking (what you convince me to, BTW). But, since there is no visible
macro/wrapper for this, people will probably mostly choose what they
can see in workqueue.h, so not necessarily the best thing.

Another question is if schedule_on_each_cpu() is really such a good
example here: it seems these "xxx && yyy" examples could be faster,
but I've lost track of this earlier thread.

BTW, flush_work() probably needs a lockdep annotation similar to
flush_workqueue().

Otherwise this all looks OK to me.

Thanks,
Jarek P.
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