linux-kernel - Re: [PATCH RFC 00/11] lock monitor: Separate features related to lock

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Date:	Wed, 17 Mar 2010 09:59:36 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	linux-kernel@...r.kernel.org, h.mitake@...il.com,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH RFC 00/11] lock monitor: Separate features related to
	lock

On Wed, Mar 17, 2010 at 10:52:30AM +0100, Ingo Molnar wrote:
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > > You add chained indirect calls into all lock ops, that's got to hurt.
> > 
> > Well, the idea was not bad at the first glance. It was separating lockdep 
> > and lock events codes.
> > 
> > But indeed, the indirect calls plus the locking are not good for such a fast 
> > path.
> 
> What would be nice to have is some sort of dynamic patching approach to enable 
> _both_ lockdep, lockstat and perf lock.
> 

right. this would allow distros to ship lockdep, lockstat in their
default kernels as a runtime option.

> If TRACE_EVENT() tracepoints were patchable we could use them. (but they arent 
> right now)
> 

right. I'm going to re-post the jump labeling work again soon, which
implicitly makes all TRACE_EVENT() tracepoints into dynamic patch
points. The jump label approach can also be deployed independently of
the tracepoints.

Also, any hints, suggestions on where to start with this type of
project? I thought a lot of the lockdep overhead was tied up in the data
structures? If its just a matter of identifying the dynamic patch
points. I can convert them to jump label and run benchmarks, pretty
easily.

thanks,

-Jason

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