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

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Date:	Thu, 13 Feb 2014 14:02:28 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Don Zickus <dzickus@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Joe Mario <jmario@...hat.com>,
	Richard Fowles <fowles@...each.com>
Subject: Re: [PATCH 00/21] perf, c2c: Add new tool to analyze cacheline
 contention on NUMA systems

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

we can add PERF_SAMPLE_REGS_KERNEL

> 
> 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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