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

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Date:	Tue, 05 Mar 2013 15:53:58 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Waiman Long <Waiman.Long@...com>,
	Davidlohr Bueso <davidlohr.bueso@...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 03/05/2013 03:52 PM, Linus Torvalds wrote:
> On Tue, Mar 5, 2013 at 11:42 AM, Waiman Long <Waiman.Long@...com> wrote:
>>
>> The recommended kernel.sem value from Oracle is "250 32000 100 128". I have
>> tried to reduce the maximum semaphores per array (1st value) while
>> increasing the max number of arrays. That tends to reduce the ipc_lock
>> contention in kernel, but it is against Oracle's recommendation.
>
> Ok, the Oracle recommendations seem to be assuming that we'd be
> scaling the semaphore locking sanely, which we don't. Since we share
> one single lock for all semaphores in the whole array, Oracle's
> recommendation does the wrong thing for our ipc_lock contention.

> David's patch should make it much easier to do the locking more
> fine-grained, and it sounds like Rik is actively working on that,

Indeed.  Though how well my patches will work with Oracle will
depend a lot on what kind of semctl syscalls they are doing.

Does Oracle typically do one semop per semctl syscall, or does
it pass in a whole bunch at once?

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