Re: [PATCH v1 1/5] perf/core: Define the common branch type classification

Peter Zijlstra
2017-04-06T16:56:33Z

On Thu, Apr 06, 2017 at 10:43:19PM +0800, Jin, Yao wrote:
>
>
> On 4/6/2017 5:25 PM, Peter Zijlstra wrote:
> > On Thu, Apr 06, 2017 at 04:21:06PM +0800, Jin, Yao wrote:
> > > Hi, otherwise we have to maintain 2 branch type copies between kernel and
> > > user-space.
> > >
> > > For example, currently X86_BR_* are defined in lbr.c. To display the branch
> > > type in user-space, the user-space has to maintain the same copy for
> > > X86_BR_*. I didn't get a better idea.
> > I still don't understand what you want; or why it would matter.
> >
> > Those specific macros are for hardware LBR filter emulation/fixup. What
> > does that have to do with any userspace crud?
>
> I just want to provide a new feature that the user can directly check branch
> type
> in perf report, instead of looking it up in the binary. Binary could be not
> available
> later, so it's possible that userspace can't get the branch type.
>
> The X86_BR are generated when disassembling the branch instruction in
> kernel.
> They can be considered as the x86 branch types.
>
> It's easy to let kernel return the x86 branch types to userspace, and then
> userspace
> shows the branch type in perf report.
>
> While kernel and userspace have to maintain the X86_BR definitions. One copy
> is in
> kernel and the other copy is in userspace. To avoid the duplicate
> definitions , I define
> the common branch type in perf_event.h to share between kernel and
> userspace.
> That's why I do that.

Argh, fix your mailer. That is unreadable.

/me reflows...

> I just want to provide a new feature that the user can directly check
> branch type in perf report, instead of looking it up in the binary.
> Binary could be not available later, so it's possible that userspace
> can't get the branch type.
>
> The X86_BR are generated when disassembling the branch instruction in
> kernel. They can be considered as the x86 branch types.
>
> It's easy to let kernel return the x86 branch types to userspace, and
> then userspace shows the branch type in perf report.
>
> While kernel and userspace have to maintain the X86_BR definitions.
> One copy is in kernel and the other copy is in userspace. To avoid the
> duplicate definitions , I define the common branch type in
> perf_event.h to share between kernel and userspace. That's why I do
> that.

See, that's so much better..

Oh, so you _ARE_ adding a kernel feature? I understood you only wanted
to change perf-report.

WTH didn't you Cc the maintainers?

Also, if you do this, you need to Cc the PowerPC people, since they too
implement PERF_SAMPLE_BRANCH_ bits.