linux-kernel - Re: [PATCH v7 0/4] perf: add support for profiling jitted code

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Date:	Thu, 1 Oct 2015 11:17:36 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com, mingo@...e.hu,
	ak@...ux.intel.com, jolsa@...hat.com, namhyung@...nel.org,
	cel@...ibm.com, dsahern@...il.com, adrian.hunter@...el.com,
	johnmccutchan@...gle.com, brendan.d.gregg@...il.com
Subject: Re: [PATCH v7 0/4] perf: add support for profiling jitted code

On Thu, Oct 01, 2015 at 08:45:44AM +0200, Stephane Eranian wrote:
> This patch series extends perf record/report/annotate to enable
> profiling of jitted (just-in-time compiled) code. The current
> perf tool provides very limited support for profiling jitted
> code for some runtime environments. But the support is experimental
> and cannot be used in complex environments. It relies on files
> in /tmp, for instance. It does not support annotate mode or
> rejitted code.
> 
> This patch series adds a better way of profiling jitted code
> with the following advantages:
>    - support any jitted code environment (some with modifications)
>    - support Java runtime with JVMTI interface with no modifications
>    - provides a portable JVMTI agent library
>    - known to support V8 runtime
>    - known to support DART runtime
>    - supports code rejitting and code movements
>    - no files in /tmp
>    - meta-data file is unique to each run
>    - no changes to perf report/annotate
>    - support per-thread and system-wide profiling
>    - support monitoring of multiple simultaneous Jit runtimes
>    - source level view in perf annotate
> 
> The support is based on cooperation with the runtime. For Java runtimes,
> supporting the JVMTI interface, there is no change necessary. For other
> runtimes, modifications are necessary to emit the meta-data to support
> symbolization, annotation, source lines correlation of the samples.
> Those modifications are relatively straighforward, some have been 
> implemented in V8 and DART.

Do V8 and DART come with these bits or will that be a future
contribution?

> This will also generate an ELF image for each jitted function. The
> injected MMAP records will point to these ELF images. The reasoning
> behind using ELF images is that it makes processing for perf report
> and annotate automatic and transparent. It also makes it easier to
> package and analyze on a remote machine. Binutils tools can decode
> the ELF images easily.

The generation of ELF files is really nice!

All in all this looks really nice.

Thanks for doing this.
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