linux-kernel - Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount

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Date:	Fri, 30 Aug 2013 09:32:02 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Sedat Dilek <sedat.dilek@...il.com>
Cc:	Waiman Long <waiman.long@...com>, Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jeff Layton <jlayton@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount

On Fri, Aug 30, 2013 at 8:38 AM, Sedat Dilek <sedat.dilek@...il.com> wrote:
>
> A Samsung series-5 ultrabook.
>
> $ grep "model name" /proc/cpuinfo | uniq
> model name      : Intel(R) Core(TM) i5-2467M CPU @ 1.60GHz

Hmm. Do you have debugging options enabled? Because that CPU should
have the same core count as mine (two+HT), a slightly smaller cache
(3M vs 4M) and runs at a noticeably lower frequency (1.6GHz vs 3.5).
It probably also has slower memory etc, but that should still make it
maybe half speed of mine. Not 1/20th.

As mentioned, I get numbers in the 65M range. Yours are under 2.7M.
Even with some thermal throttling, I would expect better than that.

My pixel (1.8GHz i5-3427U) should be a *bit* faster that yours. And I
get 54M iterations on that.

I saw you mentioned CONFIG_CMPXCHG_LOCKREF=y in your .config, so you
don't have spinlock debugging enabled, but maybe you have some other
expensive debug option enabled. Like DEBUG_PAGEALLOC etc.

If you get "perf" compiled, mind doing a

    perf record -f -e cycles:pp ./a.out
    perf report

on it and look what that says?

              Linus
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