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Date: Wed, 10 Nov 2010 17:44:16 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>, Christoph Hellwig <hch@infradead.org>,
        rostedt@goodmis.org, andi@firstfloor.org, lwoodman@redhat.com,
        linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 1/2] tracing,mm - add kernel pagefault tracepoint for
	x86 & x86_64
Message-ID: <20101110164413.GA5360@nowhere>
References: <1289390172-9730-1-git-send-email-jolsa@redhat.com> <1289390172-9730-2-git-send-email-jolsa@redhat.com> <20101110132954.GA2101@infradead.org> <20101110134436.GD1949@jolsa.brq.redhat.com> <20101110135244.GA31638@elte.hu> <20101110150021.GA5750@nowhere> <20101110151750.GA11541@jolsa.brq.redhat.com>
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On Wed, Nov 10, 2010 at 04:17:50PM +0100, Jiri Olsa wrote:
> On Wed, Nov 10, 2010 at 04:00:25PM +0100, Frederic Weisbecker wrote:
> > On Wed, Nov 10, 2010 at 02:52:44PM +0100, Ingo Molnar wrote:
> > > 
> > > * Jiri Olsa <jolsa@redhat.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.
> > 
> 
> I guess I can take the regs out then.. would that patch be acceptable
> afterwards..?


Please take out the regs yeah.

Thanks.

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