linux-kernel - Re: mapping instructions to dynamic languages like java, python, ruby

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Message-ID: <CABPqkBTNeAoW6z91q_2U+KWAXnkn3b7K6bGNc3PmRp+h89_cFw@mail.gmail.com>
Date:	Tue, 22 Apr 2014 23:24:24 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Don Zickus <dzickus@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	William Cohen <wcohen@...hat.com>
Subject: Re: mapping instructions to dynamic languages like java, python, ruby

On Tue, Apr 22, 2014 at 10:54 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> Does anyone have any thoughts or experience on this?
>
> perf has a JIT interface today, but it's extremely primitive
> and only supports symbols. Clearly it could be done better.
>
> Various JITs (e.g. Java) have special debug interfaces for this.
>
> Various non perf profilers support it too. e.g. Vtune has a special
> API for it:
> https://software.intel.com/sites/default/files/jit_profiling_api_lin_0.pdf
>
> Essentially you would need to write a JIT specific adapter
> that translates to perf format. Or emulate the Vtune interface
> and reuse existing Vtune adaptations.
>
> perf record needs some kind of side band interface where the JIT adapter
> can report to it:
> - symbols
> - the assembler code (so it can be shown)
> - source lines
> - report any changes when JITed code changes
>
Forgot to mention that my implementation does go all the way to jitted
code assembly view via perf annotate + source view.

So it does cover all aspects.

As for attaching to a running JIT, this again needs some cooperation
from JIT environment.


> Then perf record could put that information into the perf.data.
>
> In theory that information could be passed through the kernel,
> but just using some user protocol (unix sockets or files) would be
> likely enough. The current interface uses files in /tmp.
> I would likely change that, it's not clear even if it's secure.
>
> It's likely a substantial project.
>
> It would be even useful for the kernel, as the kernel does JITing
> itself these days.
>
> -Andi
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