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Date: Sun, 1 Sep 2013 08:32:34 -0700
Message-ID: <CA+55aFwU054C+zC+G+JrF4ngWvVmvD9WPGWaT_2=nF2j7bpHxA@mail.gmail.com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Waiman Long <waiman.long@hp.com>, Ingo Molnar <mingo@kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        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>
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On Sun, Sep 1, 2013 at 3:01 AM, Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> Looks like this is now 10x faster: ~2.66Mloops (debug) VS.
> ~26.60Mloops (no-debug).

Ok, that's getting to be in the right ballpark.

But your profile is still odd.

> Samples: 159K of event 'cycles:pp', Event count (approx.): 76968896763
>  12,79%  t_lockref_from-  [kernel.kallsyms]     [k] irq_return
>   4,36%  t_lockref_from-  [kernel.kallsyms]     [k] __ticket_spin_lock

If you do the profile with "-g", what are the top callers of this? You
shouldn't see any spinlock load from the path lookup, but you have all
these other things going on..

>   4,36%  t_lockref_from-  [kernel.kallsyms]     [k] __acct_update_integrals
>   4,07%  t_lockref_from-  [kernel.kallsyms]     [k] user_exit
>   3,12%  t_lockref_from-  [kernel.kallsyms]     [k] local_clock
>   2,83%  t_lockref_from-  [kernel.kallsyms]     [k] lockref_get_or_lock
>   2,73%  t_lockref_from-  [kernel.kallsyms]     [k] kmem_cache_alloc
>   2,62%  t_lockref_from-  [kernel.kallsyms]     [k] __d_lookup_rcu

You're spending more time on the task stats than on the actual lookup.
Maybe you should turn off CONFIG_TASKSTATS..But why that whole
irq_return thing? Odd.

                   Linus
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