linux-kernel - Re: [PATCH] lock stat for -rt 2.6.20-rc2-rt2.2.lock

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Date:	Wed, 3 Jan 2007 16:12:26 -0800
From:	Bill Huey (hui) <billh@...ppy.monkey.org>
To:	"Chen, Tim C" <tim.c.chen@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Walker <dwalker@...sta.com>,
	"Bill Huey (hui)" <billh@...ppy.monkey.org>
Subject: Re: [PATCH] lock stat for -rt 2.6.20-rc2-rt2.2.lock_stat.patch

On Wed, Jan 03, 2007 at 03:59:28PM -0800, Chen, Tim C wrote:
> Bill Huey (hui) wrote:
> http://mmlinux.sourceforge.net/public/patch-2.6.20-rc2-rt2.2.lock_stat.patch
> 
> This version is much better and ran stablely.  
> 
> If I'm reading the output correctly, the locks are listed by 
> their initialization point (function, file and line # that a lock is
> initialized).  
> That's good information to identify the lock.  

Yes, that's correct.

Good to know that. What did the output reveal ?

It can be extended by pid/futex for userspace app that has yet to be done.
It might require changes to glibc or a some kind of dynamic tracing to
communicate to kernel space information about that lock. There are other
kernel uses as well. It's just a basic mechanisms for a variety of uses.
This patch has some LTT and Dtrace-isms to it.

What's your intended use again summarized ? futex contention ? I'll read
the first posting again.

> However, it will be more useful if there is information about where the
> locking
> was initiated from and who was trying to obtain the lock.

It would add quite a bit more overhead, but it could be done with lockdep
directly I believe in conjunction with this patch. However, it should be
specific enough though that a kernel code examination at the key points
of all users of the lock would show where the problem places are as well
as users.

bill

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