Re: [PATCH 00/21] perf, c2c: Add new tool to analyze cacheline contention on NUMA systems

[Stephane Eranian]

On Thu, Feb 13, 2014 at 2:02 PM, Jiri Olsa <jolsa@xxxxxxxxxx> 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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