linux-kernel - Re: [PATCH 1/2] ipc semaphores: reduce ipc

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Message-ID: <20100413200527.GG5683@laptop>
Date:	Wed, 14 Apr 2010 06:05:27 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Chris Mason <chris.mason@...cle.com>,
	Manfred Spraul <manfred@...orfullife.com>,
	zach.brown@...cle.com, jens.axboe@...cle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] ipc semaphores: reduce ipc_lock contention in
 semtimedop

On Tue, Apr 13, 2010 at 03:38:01PM -0400, Chris Mason wrote:
> On Wed, Apr 14, 2010 at 05:25:51AM +1000, Nick Piggin wrote:
> > I didn't notice anything that should make that go faster?
> 
> Since I'm avoiding the ipc lock while operating on the array, it'll help
> any workload that hits on two or more semaphores in the array at
> once.

Yeah, I don't think SAP did that, significantly to matter. Possibly
some (aside from Oracle of course), do though.


> > Yes, with such a workload, using semops is basically legacy and simple
> > mutexes should work better. So I'm not outright against improving sysv
> > sem performance for more complex cases where nothing else we have works
> > as well.
> > 
> 
> I'm not in a hurry to overhaul a part of the kernel that has been stable
> for a long time.  But it really needs some love I think.  I'll have more
> numbers from a tpc run later this week.

Yep, I'm not against it. "industry standard benchmark" numbers would
be great.

I do think we need to be really careful with semantics though. The
API's been around for long enough that it is going to have been
(ab)used in every way possible :)

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