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

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Message-ID: <CA+icZUXi-YHK23sKnVQbfi4K2FOVZiROQ76H5Qw2NxTJT2uzDQ@mail.gmail.com>
Date:	Wed, 4 Sep 2013 00:37:25 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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 Sun, Sep 1, 2013 at 5:32 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Sun, Sep 1, 2013 at 3:01 AM, Sedat Dilek <sedat.dilek@...il.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.
>

[ init/Kconfig ]
...
config TASKSTATS
        bool "Export task/process statistics through netlink"
        depends on NET <--- Difficult to disable it?!
        default n
        help
          Export selected statistics for tasks/processes through the
          generic netlink interface. Unlike BSD process accounting, the
          statistics are available during the lifetime of tasks/processes as
          responses to commands. Like BSD accounting, they are sent to user
          space on task exit.

          Say N if unsure.
...

- Sedat -
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