Support instruction-level perf event profiling to Dart VM using V8's ll_prof.py.

Support instruction-level perf event profiling to Dart VM using V8's ll_prof.py.

Usage:

1) perf record -g out/ReleaseIA32/dart --ll-prof example.dart
2) third_party/v8/tools/ll_prof.py --disasm-top=3

This will produce a  per-function and a per-instruction profile with 
disassembly for the top 3 function in the profile.

Currently only available on Linux.
Committed: https://code.google.com/p/dart/source/detail?r=19044

[Vyacheslav Egorov (Google), 2013-02-26 14:19:25]

lgtm

https://codereview.chromium.org/12342012/diff/2002/runtime/vm/os_linux.cc
File runtime/vm/os_linux.cc (right):

https://codereview.chromium.org/12342012/diff/2002/runtime/vm/os_linux.cc#new...
runtime/vm/os_linux.cc:47: const char* filename = "v8.log.ll";
I like the name. 

You can consider making ll_prof.py more generic to handle both Dart and V8. 

You can also write the tag denoting type of the runtime into the stream.

https://codereview.chromium.org/12342012/diff/2002/runtime/vm/os_linux.cc#new...
runtime/vm/os_linux.cc:85: void LowLevelLogWriteStruct(const T& s) {
There is only a single structure so for now we don't need templated version.

However I understand that this code was taken from the V8 where multiple events
exist.

[Vyacheslav Egorov (Google), 2013-02-26 14:24:17]

one more comment

https://codereview.chromium.org/12342012/diff/2002/runtime/vm/os_linux.cc
File runtime/vm/os_linux.cc (right):

https://codereview.chromium.org/12342012/diff/2002/runtime/vm/os_linux.cc#new...
runtime/vm/os_linux.cc:102: const char* format = "%s%s";
Use Zone::PrintToString here.

[Florian Schneider, 2013-02-26 14:31:50]

Thanks. Fixed x64. Landing...

On 2013/02/26 14:24:17, Vyacheslav Egorov (Google) wrote:
> one more comment
> 
> https://codereview.chromium.org/12342012/diff/2002/runtime/vm/os_linux.cc
> File runtime/vm/os_linux.cc (right):
> 
>
https://codereview.chromium.org/12342012/diff/2002/runtime/vm/os_linux.cc#new...
> runtime/vm/os_linux.cc:102: const char* format = "%s%s";
> Use Zone::PrintToString here.

[Florian Schneider, 2013-02-26 14:38:10]

Committed patchset #3 manually as r19044 (presubmit successful).