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    SubjectRe: [PATCH 00/21] perf, c2c: Add new tool to analyze cacheline contention on NUMA systems
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    On Thu, Feb 13, 2014 at 2:02 PM, Jiri Olsa <jolsa@redhat.com> wrote:
    > On Tue, Feb 11, 2014 at 08:50:13AM -0300, Arnaldo Carvalho de Melo wrote:
    >> Em Tue, Feb 11, 2014 at 12:14:21PM +0100, Peter Zijlstra escreveu:
    >> > On Tue, Feb 11, 2014 at 12:08:56PM +0100, Stephane Eranian wrote:
    >> > > Assuming you can decode and get the info about the base registers used,
    >> > > you'd have to do this for each arch with load/store sampling capabilities.
    >> > > this is painful compared to getting the portable info from dwarf directly.
    >>
    >> > But its useful now, as compared to whenever GCC gets around to
    >> > implementing more dwarves and that GCC getting used widely enough to
    >> > actually rely on it.
    >>
    >> > All you need for the decode is a disassembler, and every arch should
    >> > already have multiple of those. Should be easy to reuse one, right?
    >>
    >> Yeah, I never got around to actually try to implement this, but my
    >> feeling was that all the bits and pieces were there already:
    >>
    >> 1) the precise IP for the instruction, that disassembled would tell
    >> which registers were being operated on, or memory that we would "reverse
    >> map" to a register
    >>
    >> 2) DWARF expression locations that allows us to go from registers to a
    >> variable/parameter and thus to a type
    >>
    >> 3) PERF_SAMPLE_REGS_USER (from a quick look, why do we have "USER" in
    >> it? Jiri?)
    >
    > well, it was meant for store user registers only
    > to assists user DWARF unwind
    >
    But it does captures the user state regardless of the stack snapshotting.

    > we can add PERF_SAMPLE_REGS_KERNEL
    >
    I have a patch series to do this and more. It will be ready next month
    hopefully.

    >>
    >> 4) libunwind have register maps for various arches, so probably
    >> something there could be reused here as well (Jiri?)
    >
    > not sure what you mean by 'something' here.. but yep,
    > libunwind does have register maps for various arches
    >
    > jirka


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