linux-kernel - Re: [PATCH v2 0/4] ipc: reduce ipc lock contention

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Date:	Tue, 5 Mar 2013 07:40:51 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
Cc:	Rik van Riel <riel@...hat.com>,
	Emmanuel Benisty <benisty.e@...il.com>,
	"Vinod, Chegu" <chegu_vinod@...com>,
	"Low, Jason" <jason.low2@...com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>, aquini@...hat.com,
	Michel Lespinasse <walken@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Larry Woodman <lwoodman@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 0/4] ipc: reduce ipc lock contention

On Tue, Mar 5, 2013 at 1:35 AM, Davidlohr Bueso <davidlohr.bueso@...com> wrote:
>
> The following set of patches are based on the discussion of holding the
> ipc lock unnecessarily, such as for permissions and security checks:

Ok, looks fine from a quick look (but then, so did your previous patch-set ;)

You still open-code the spinlock in at least a few places (I saw
sem_getref), but I still don't care deeply.

>> 2) While on an Oracle swingbench DSS (data mining) workload the
> improvements are not as exciting as with Rik's benchmark, we can see
> some positive numbers. For an 8 socket machine the following are the
> percentages of %sys time incurred in the ipc lock:

Ok, I hoped for it being more noticeable. Since that benchmark is less
trivial than Rik's, can you do a perf record -fg of it and give a more
complete picture of what the kernel footprint is - and in particular
who now gets that ipc lock function? Is it purely semtimedop, or what?
Look out for inlining - ipc_rcu_getref() looks like it would be
inlined, for example.

It would be good to get a "top twenty kernel functions" from the
profile, along with some call data on where the lock callers are.. I
know that Rik's benchmark *only* had that one call-site, I'm wondering
if the swingbench one has slightly more complex behavior...

                 Linus
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