Re: [PATCH] perf/x86/intel/pt: Allow disabling branch tracing

Andi Kleen
2017-02-06T15:58:28Z

Alexander Shishkin <alexander.shishkin@linux.intel.com> writes:

> Now that Intel PT supports more types of trace content than just branch
> tracing, it may be useful to allow the user to disable branch tracing
> when it is not needed.
>
> The special case is BDW, where not setting BranchEn is not supported.
>
> This is slightly trickier than necessary, because up to this moment
> the driver has been setting BranchEn automatically and the userspace
> assumes as much. Instead of reversing the semantics of BranchEn, we
> introduce a 'passthrough' bit, which will forego the default and allow
> the user to set BranchEn to their heart's content.

cpu/passthrough=1,branchen=1/ seems far uglier/more complicanted to me
than the original cpu/nobranch=1/

Just think how you would explain it to the user in the manpage.

-Andi