Re: [PATCH 1/2] tracing,mm - add kernel pagefault tracepoint for x86 & x86_64

Frederic Weisbecker
2010-11-10T16:44:26Z

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.