linux-kernel - Re: [PATCH 25/25] ipc: don't use [delayed_]work

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Date:	Fri, 21 Dec 2012 18:22:10 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 25/25] ipc: don't use [delayed_]work_pending()

Hello, Andrew.

On Fri, Dec 21, 2012 at 06:15:23PM -0800, Andrew Morton wrote:
> On Fri, 21 Dec 2012 17:57:15 -0800 Tejun Heo <tj@...nel.org> wrote:
> 
> > There's no need to test whether a (delayed) work item in pending
> > before queueing, flushing or cancelling it.  Most uses are unnecessary
> > and quite a few of them are buggy.
> 
> > -		if (!work_pending(&ipc_memory_wq))
> > -			schedule_work(&ipc_memory_wq);
> > +		schedule_work(&ipc_memory_wq);
> 
> Well, the new code is a ton slower than the old code if the work is
> frequently pending, so some care is needed with such a conversion.

Yeah, I mentioned it in the head message.  it comes down to
test_and_set_bit() vs. test_bit() and none of the current users seems
to be hot enough for that to matter at all.

In very hot paths, such optimization *could* be valid.  The problem is
that [delayed_]work_pending() seem to be abused much more than they
are put to any actual usefulness.  Maybe we should rename them to
something really ugly.  I don't know.

> That's not an issue for the IPC callsite - memory offlining isn't
> frequent.
> 
> > ...
> >
> > Please let me know how this patch should be routed.  I can take it
> > through the workqueue tree if necessary.
> > 
> 
> Please merge this one yourself.

Can I add your acked-by?

Thanks.

-- 
tejun
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