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    SubjectRe: [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@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.



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