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

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Date:	Fri, 20 May 2011 09:20:34 +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>, trivial@...nel.org
Subject: Re: [RESEND PATCH] Documentation: statistics about nested locks

On Thu, May 19, 2011 at 6:53 PM, Juri Lelli <juri.lelli@...il.com> wrote:
> Explain what the trailing "/1" on some lock class names of lock_stat output
> means.
>
> Cc: Yong Zhang <yong.zhang0@...il.com>
> Signed-off-by: Juri Lelli <juri.lelli@...il.com>
>

Looks good.

Reviewed-by: Yong Zhang <yong.zhang0@...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 second subclass (/1) of &rq->lock class
> +(subclass starts from 0), 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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