Message-ID: <51365B66.5010905@redhat.com>
Date: Tue, 05 Mar 2013 15:53:58 -0500
From: Rik van Riel <riel@redhat.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Waiman Long <Waiman.Long@hp.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>,
        Emmanuel Benisty <benisty.e@gmail.com>,
        "Vinod, Chegu" <chegu_vinod@hp.com>, "Low, Jason" <jason.low2@hp.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andrew Morton <akpm@linux-foundation.org>, aquini@redhat.com,
        Michel Lespinasse <walken@google.com>, Ingo Molnar <mingo@kernel.org>,
        Larry Woodman <lwoodman@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v2 0/4] ipc: reduce ipc lock contention
References: <1362476149.2225.50.camel@buesod1.americas.hpqcorp.net> <513626E9.2040509@redhat.com> <51364AB9.80206@hp.com> <CA+55aFwYOUyG_DQUqVPrQNi_a=AUwS53U-Yi6jbvJTGRxQ_aEQ@mail.gmail.com>
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On 03/05/2013 03:52 PM, Linus Torvalds wrote:
> On Tue, Mar 5, 2013 at 11:42 AM, Waiman Long <Waiman.Long@hp.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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