Date: Tue, 3 Sep 2013 16:08:08 +0200
From: Pavel Machek <pavel@ucw.cz>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>,
        Sedat Dilek <sedat.dilek@gmail.com>, Waiman Long <waiman.long@hp.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Jeff Layton <jlayton@redhat.com>, Miklos Szeredi <mszeredi@suse.cz>,
        Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>, Andi Kleen <andi@firstfloor.org>,
        "Chandramouleeswaran, Aswin" <aswin@hp.com>,
        "Norton, Scott J" <scott.norton@hp.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Arnaldo Carvalho de Melo <acme@infradead.org>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount
Message-ID: <20130903140808.GA14734@amd.pavel.ucw.cz>
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 <CA+55aFzsXwFkYsWY45ZNTaVFC+-1Yh9nxx=NLhv+NxGmQAKHTg@mail.gmail.com>
 <20130901233005.GX13318@ZenIV.linux.org.uk>
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Hi!

> It is entirely possible that it is just a "cycles:pp" oddity - because
> the "lock xadd" is serializing, it can't retire until everything
> around it has been sorted out, and maybe it just shows up in profiles
> more than is really "fair" to the instruction itself, because it ends
> up being that stable point for potentially hundreds of instructions
> around it.

Hmm, turn "lock xadd" into plain add, and see if it improves loops per
second? Preferably on scratch filesystem, because you may corrupt it...
									Pavel
-- 
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