llvm dev - Jul 2018 - profiling JIT compiled code with perf

Hello,

is there any support in LLVM for the jitdump format [1] of perf?

It enables perf report to also "zoom in" and annotate the JIT compiled
code on assembly level with runtime percentage. It helps a lot to
understand which parts of the generated code is the bottleneck.

I recently did a proof-of-concept for the JIT assembler asmjit [2]. It
just dumps the generated code in the right format and mmaps the file to
let perf record know about it. perf report picks it up automatically.

So, is there any profiling support for JIT compiled code?

Best regards,
Frank


[1]
https://raw.githubusercontent.com/torvalds/linux/master/tools/perf/Documentation/jitdump-specification.txt
[2] https://github.com/asmjit/asmjit/pull/197

> Hello,
> 
> is there any support in LLVM for the jitdump format [1] of perf?
> 
> It enables perf report to also "zoom in" and annotate the JIT
compiled
> code on assembly level with runtime percentage. It helps a lot to
> understand which parts of the generated code is the bottleneck.
> 
> I recently did a proof-of-concept for the JIT assembler asmjit [2]. It
> just dumps the generated code in the right format and mmaps the file
> to let perf record know about it. perf report picks it up
> automatically.
> 
> So, is there any profiling support for JIT compiled code?

I guess that's a no.

Is there a simple way to get a pointer to the assemble code and the
exact size in bytes? Or should I just use the function pointer? Where
do I get the size?

Then I could at least dump the native code. Profiling on assembly level
would already help a lot.

Regards,
Frank

Have you seen https://reviews.llvm.org/D44892? we are using it in Julia to
use perf on jitted code.

-Valentin

On Wed, 18 Jul 2018 at 17:13 Frank Tetzel via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> > Hello,
> >
> > is there any support in LLVM for the jitdump format [1] of perf?
> >
> > It enables perf report to also "zoom in" and annotate the
JIT compiled
> > code on assembly level with runtime percentage. It helps a lot to
> > understand which parts of the generated code is the bottleneck.
> >
> > I recently did a proof-of-concept for the JIT assembler asmjit [2]. It
> > just dumps the generated code in the right format and mmaps the file
> > to let perf record know about it. perf report picks it up
> > automatically.
> >
> > So, is there any profiling support for JIT compiled code?
>
>
> I guess that's a no.
>
> Is there a simple way to get a pointer to the assemble code and the
> exact size in bytes? Or should I just use the function pointer? Where
> do I get the size?
>
> Then I could at least dump the native code. Profiling on assembly level
> would already help a lot.
>
> Regards,
> Frank
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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