linux-kernel - Re: [PATCH] Documentation: statistics about nested locks

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Date:	Tue, 17 May 2011 10:00:12 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Juri Lelli <juri.lelli@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] Documentation: statistics about nested locks

On Mon, May 16, 2011 at 6:01 PM, Juri Lelli <juri.lelli@...il.com> wrote:
> Hi all,
> just a little patch to the Documentation. I had some trouble understanding
> the trailing "/1" on some lock class names of lock_stat output, so I added
> something on this inside lockstat documentation.
>
> Signed-off-by: Juri Lelli <juri.lelli@...il.com>
>
> ---
>  Documentation/lockstat.txt |   36 ++++++++++++++++++++++++++++++++++--
>  1 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/lockstat.txt b/Documentation/lockstat.txt
> index 65f4c79..75eeb65 100644
> --- a/Documentation/lockstat.txt
> +++ b/Documentation/lockstat.txt
> @@ -12,8 +12,9 @@ Because things like lock contention can severely impact
> performance.
>  - HOW
>
>  Lockdep already has hooks in the lock functions and maps lock instances to
> -lock classes. We build on that. The graph below shows the relation between
> -the lock functions and the various hooks therein.
> +lock classes. We build on that (see Documentation/lockdep-design.txt).
> +The graph below shows the relation between the lock functions and the
> various
> +hooks therein.
>
>         __acquire
>             |
> @@ -128,6 +129,37 @@ points are the points we're contending with.
>
>  The integer part of the time values is in us.
>
> +Dealing with nested locks, subclasses may appear:
> +
> +32...............................................................................................................................................................................................
> +33
> +34                               &rq->lock:         13128 13128
> 0.43         190.53      103881.26          97454  3453404           0.00
>       401.11    13224683.11
> +35                               ---------
> +36                               &rq->lock            645
> [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
> +37                               &rq->lock            297
> [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
> +38                               &rq->lock            360
> [<ffffffff8103c4c5>] select_task_rq_fair+0x1f0/0x74a
> +39                               &rq->lock            428
> [<ffffffff81045f98>] scheduler_tick+0x46/0x1fb
> +40                               ---------
> +41                               &rq->lock             77
> [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
> +42                               &rq->lock            174
> [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
> +43                               &rq->lock           4715
> [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
> +44                               &rq->lock            893
> [<ffffffff81340524>] schedule+0x157/0x7b8
> +45
> +46...............................................................................................................................................................................................
> +47
> +48                             &rq->lock/1:         11526 11488
> 0.33         388.73      136294.31          21461    38404           0.00
>        37.93      109388.53
> +49                             -----------
> +50                             &rq->lock/1          11526
> [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
> +51                             -----------
> +52                             &rq->lock/1           5645
> [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
> +53                             &rq->lock/1           1224
> [<ffffffff81340524>] schedule+0x157/0x7b8
> +54                             &rq->lock/1           4336
> [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
> +55                             &rq->lock/1            181
> [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
> +
> +Line 48 shows statistics for the first subclass (/1) of &rq->lock class,

Actually it's the second subclass because subclass starts from 0.

Thanks,
Yong

> since
> +in this case, as line 50 suggests, double_rq_lock actually acquires a
> nested
> +lock of two spinlocks.
> +
>  View the top contending locks:
>
>  # grep : /proc/lock_stat | head
> --
> 1.7.4.1
>



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