linux-kernel - Re: [tip:core/locking] x86/smp: Move waiting on contended ticket lock out of line

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Message-ID: <CA+55aFygzjuNYiG4MTPMzimEjQ92rpS-rNJr7HD4OQCAqze5zg@mail.gmail.com>
Date:	Wed, 27 Feb 2013 20:49:01 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
Cc:	Rik van Riel <riel@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Vinod, Chegu" <chegu_vinod@...com>,
	"Low, Jason" <jason.low2@...com>,
	linux-tip-commits@...r.kernel.org,
	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>
Subject: Re: [tip:core/locking] x86/smp: Move waiting on contended ticket lock
 out of line

On Wed, Feb 27, 2013 at 8:06 PM, Davidlohr Bueso <davidlohr.bueso@...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.

          Linus
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