perf branch

perf branch

[Noah Luther]

Hello,

I am trying to use perf to trace branches as described by the 'perf
branch' subcommand. Is there support through perf_event_open to access
the buffer storing branch traces? I saw Akihiro Nagai's presentation
on 'perf branch', but haven't yet figured out how to enable BTS and
access the buffer based on the documentation on this page:

http://web.eece.maine.edu/~vweaver/projects/perf_events/perf_event_open.html

If there are any resources that might be of use to me, I would
appreciate any assistance.

Thank you,
Noah

Re: perf branch

[Christopher Covington]

Hi Noah,

On 04/13/2014 11:55 PM, Noah Luther wrote:
> Hello,
> 
> I am trying to use perf to trace branches as described by the 'perf
> branch' subcommand. Is there support through perf_event_open to access
> the buffer storing branch traces? I saw Akihiro Nagai's presentation
> on 'perf branch', but haven't yet figured out how to enable BTS and
> access the buffer based on the documentation on this page:
> 
> http://web.eece.maine.edu/~vweaver/projects/perf_events/perf_event_open.html
> 
> If there are any resources that might be of use to me, I would
> appreciate any assistance.

In the past I've found the test suite to be a useful reference. Here's a test
that looks like it might serve as a jumping-off point.

https://github.com/deater/perf_event_tests/blob/master/tests/record_sample/sample_branch_stack.c

Regards,
Christopher

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by the Linux Foundation.

Re: perf branch

[Andi Kleen]

Noah Luther <nluther@vt.edu> writes:

> Hello,
>
> I am trying to use perf to trace branches as described by the 'perf
> branch' subcommand. Is there support through perf_event_open to access
> the buffer storing branch traces? I saw Akihiro Nagai's presentation
> on 'perf branch', but haven't yet figured out how to enable BTS and
> access the buffer based on the documentation on this page:
>
> http://web.eece.maine.edu/~vweaver/projects/perf_events/perf_event_open.html
>
> If there are any resources that might be of use to me, I would
> appreciate any assistance.

perf branch never made it, but you can use 

perf record -e branches:u -c1 ...
perf script

Also the latest GDB snapshots have builtin support for BTS through
perf in a somewhat more convenient interface.

Keep in mind that BTS is quite slow and often cannot keep up.
In the future ProcessorTrace will be better.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only