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

Ingo Molnar
2010-11-10T13:53:03Z

* 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