linux-kernel - Re: Lockdep usage

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Message-ID: <20100422070625.GA17515@windriver.com>
Date:	Thu, 22 Apr 2010 15:06:25 +0800
From:	Yong Zhang <yong.zhang@...driver.com>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	"lkml, " <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Lockdep usage

On Wed, Apr 21, 2010 at 11:26:07PM -0700, Darren Hart wrote:
> I'm having some trouble with lockstat. I've enabled
> CONFIG_LOCK_STATS and then run the following commands to collect the
> lock statistics for the futex_lock test case. I expect this test
> case to generate a fair amount of contention on the futex hash
> bucket locks, but they don't show up in the stats (in fact, nothing
> shows up in the stats). I have seen much longer lock_stat files when
> I forgot to clear them before the test, but no hb locks showed up
> there either.
> 
> Is my usage below incorrect? Do I have to somehow annotate the
> hb->lock in order for lockstat to track it?

IMHO, you don't need to do that.

> lock.lockstat; echo 0 > /proc/sys/kernel/lock_stat
> futex_lock: Measure FUTEX_LOCK operations per second
>         Arguments: iterations=10000000 threads=256 adaptive=no
>                    period=1000 duty-cycle=20%
> Result: 731 Kiter/s
> 
> # cat lock.lockstat
> lock_stat version 0.3
> *WARNING* lock debugging disabled!! - possibly due to a lockdep warning

This means lockdep has detect there is something wrong.
Can you show your 'dmesg'?

Thanks,
Yong

> -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>                               class name    con-bounces
> contentions   waittime-min   waittime-max waittime-total
> acq-bounces acquisitions   holdtime-min   holdtime-max
> holdtime-total
> -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> 
> #
> 
> Thanks,
> 
> -- 
> Darren Hart
> IBM Linux Technology Center
> Real-Time Linux Team
> --
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