linux-kernel - Re: [PATCH 1/2] tracing,mm - add kernel pagefault tracepoint for x86 & x86

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Message-ID: <20101110150021.GA5750@nowhere>
Date:	Wed, 10 Nov 2010 16:00:25 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Christoph Hellwig <hch@...radead.org>, rostedt@...dmis.org,
	andi@...stfloor.org, lwoodman@...hat.com,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 1/2] tracing,mm - add kernel pagefault tracepoint for
	x86 & x86_64

On Wed, Nov 10, 2010 at 02:52:44PM +0100, Ingo Molnar wrote:
> 
> * Jiri Olsa <jolsa@...hat.com> wrote:
> 
> > On Wed, Nov 10, 2010 at 08:29:54AM -0500, Christoph Hellwig wrote:
> > > On Wed, Nov 10, 2010 at 12:56:11PM +0100, Jiri Olsa wrote:
> > > > +	TP_printk("task=%lx, address=%lx, regs=%lx",
> > > > +		(unsigned long)__entry->task, (unsigned long)__entry->address,
> > > > +			__entry->regs)
> > > 
> > > How exactly do you use the information in this trace point?  Especially
> > > the undecoded pt_regs doesn't seem very useful to me at all.
> > 
> > agreed, the registers pointer are not very useful in the trace file output,
> > and could be taken away.. just wanted to be complete I guess
> > 
> > but I believe they are useful when you register the mm_kernel_pagefault
> > tracepoint and process the information by yourself
> 
> That would be expressed in a better and more generic fashion via adding 
> PERF_SAMPLE_REGS to perf_event_sample_format, and add a ptregs dump in 
> kernel/perf_event.c, perf_output_sample(). That way any tracepoint can request a 
> (user-space)ptregs state snapshot, not just the pagefault ones.
> 
> Thanks,
> 
> 	Ingo


We are going to have that with the dwarf based callchain patchset. I'm cooking
this.

Thanks.

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