From: Rik van Riel <riel@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
"Vinod, Chegu" <chegu_vinod@hp.com>,
"Low, Jason" <jason.low2@hp.com>,
linux-tip-commits@vger.kernel.org,
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>
Subject: Re: [tip:core/locking] x86/smp: Move waiting on contended ticket lock out of line
Date: Thu, 28 Feb 2013 10:13:45 -0500 [thread overview]
Message-ID: <512F7429.4020103@redhat.com> (raw)
In-Reply-To: <CA+55aFygzjuNYiG4MTPMzimEjQ92rpS-rNJr7HD4OQCAqze5zg@mail.gmail.com>
On 02/27/2013 11:49 PM, Linus Torvalds wrote:
> On Wed, Feb 27, 2013 at 8:06 PM, Davidlohr Bueso <davidlohr.bueso@hp.com> wrote:
>>
>> The attached file shows how the amount of sys time used by the ipc lock
>> for a 4 and 8 socket box.
>
> I have to say, even with the improvements, that looks pretty
> disgusting. It really makes me wonder if that thing couldn't be done
> better some way. Is it the SysV semaphores that this all ends up
> using, or what?
>
> That said, I think the IPC layer is just about the perfect candidate
> for things like this, because I'm afraid that nobody is ever going to
> fix it.
There's more to it than that. Userspace expects the IPC layer
to provide exclusion and/or serialization. That makes it a
rather poor candidate for parallelism.
Btw, the IPC lock is already fairly fine grained. One ipc
lock is allocated for each set of semaphores allocated through
sys_semget. Looking up those semaphores in the namespace, when
they are used later, is done under RCU.
next prev parent reply other threads:[~2013-02-28 15:15 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-06 20:03 [PATCH -v5 0/5] x86,smp: make ticket spinlock proportional backoff w/ auto tuning Rik van Riel
2013-02-06 20:04 ` [PATCH -v5 1/5] x86,smp: move waiting on contended ticket lock out of line Rik van Riel
2013-02-13 12:06 ` [tip:core/locking] x86/smp: Move " tip-bot for Rik van Riel
2013-02-13 16:20 ` Linus Torvalds
2013-02-13 18:30 ` Linus Torvalds
2013-02-14 0:54 ` H. Peter Anvin
2013-02-14 1:31 ` Linus Torvalds
2013-02-14 1:56 ` H. Peter Anvin
2013-02-14 10:50 ` Ingo Molnar
2013-02-14 16:10 ` Linus Torvalds
2013-02-15 15:57 ` Ingo Molnar
2013-02-15 6:48 ` Benjamin Herrenschmidt
2013-02-13 19:08 ` Rik van Riel
2013-02-13 19:36 ` Linus Torvalds
2013-02-13 22:21 ` Rik van Riel
2013-02-13 22:40 ` Linus Torvalds
2013-02-13 23:41 ` Rik van Riel
2013-02-14 1:21 ` Linus Torvalds
2013-02-14 1:46 ` Linus Torvalds
2013-02-14 10:43 ` Ingo Molnar
2013-02-27 16:42 ` Rik van Riel
2013-02-27 17:10 ` Linus Torvalds
2013-02-27 19:53 ` Rik van Riel
2013-02-27 20:18 ` Linus Torvalds
2013-02-27 21:55 ` Rik van Riel
[not found] ` <CA+55aFwa0EjGG2NUDYVLVBmXJa2k81YiuNO2yggk=GLRQxhhUQ@mail.gmail.com>
2013-02-28 2:58 ` Rik van Riel
2013-02-28 3:19 ` Linus Torvalds
2013-02-28 4:06 ` Davidlohr Bueso
2013-02-28 4:49 ` Linus Torvalds
2013-02-28 15:13 ` Rik van Riel [this message]
2013-02-28 18:22 ` Linus Torvalds
2013-02-28 20:26 ` Linus Torvalds
2013-02-28 21:14 ` Rik van Riel
2013-02-28 21:58 ` Linus Torvalds
2013-02-28 22:38 ` Rik van Riel
2013-02-28 23:09 ` Linus Torvalds
2013-03-01 6:42 ` Rik van Riel
2013-03-01 18:18 ` Davidlohr Bueso
2013-03-01 18:50 ` Rik van Riel
2013-03-01 18:52 ` Linus Torvalds
2013-02-06 20:04 ` [PATCH -v5 2/5] x86,smp: proportional backoff for ticket spinlocks Rik van Riel
2013-02-13 12:07 ` [tip:core/locking] x86/smp: Implement " tip-bot for Rik van Riel
2013-02-06 20:05 ` [PATCH -v5 3/5] x86,smp: auto tune spinlock backoff delay factor Rik van Riel
2013-02-13 12:08 ` [tip:core/locking] x86/smp: Auto " tip-bot for Rik van Riel
2013-02-06 20:06 ` [PATCH -v5 4/5] x86,smp: keep spinlock delay values per hashed spinlock address Rik van Riel
2013-02-13 12:09 ` [tip:core/locking] x86/smp: Keep " tip-bot for Eric Dumazet
2013-02-06 20:07 ` [PATCH -v5 5/5] x86,smp: limit spinlock delay on virtual machines Rik van Riel
2013-02-07 11:11 ` Ingo Molnar
2013-02-07 21:24 ` [PATCH fix " Rik van Riel
2013-02-13 12:10 ` [tip:core/locking] x86/smp: Limit " tip-bot for Rik van Riel
2013-02-07 11:25 ` [PATCH -v5 5/5] x86,smp: limit " Stefano Stabellini
2013-02-07 11:59 ` Raghavendra K T
2013-02-07 13:28 ` Rik van Riel
2013-02-06 20:08 ` [PATCH -v5 6/5] x86,smp: add debugging code to track spinlock delay value Rik van Riel
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