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

Jiri Olsa
2010-11-10T15:18:21Z

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..?

thanks,
jirka