Re: [PATCH 01/10] perf/core, x86: Add PERF_SAMPLE_LBR_TOS

[Liang, Kan]

On 10/8/2019 4:31 AM, Peter Zijlstra wrote:
> On Mon, Oct 07, 2019 at 10:59:01AM -0700, kan.liang@xxxxxxxxxxxxxxx wrote:
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 61448c19a132..ee9ef0c4cb08 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -100,6 +100,7 @@ struct perf_raw_record {
> >    */
> >   struct perf_branch_stack {
> >   	__u64				nr;
> > +	__u64				tos;
> >   	struct perf_branch_entry	entries[0];
> >   };
> >   
> > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > index bb7b271397a6..fe36ebb7dc2e 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -141,8 +141,9 @@ enum perf_event_sample_format {
> >   	PERF_SAMPLE_TRANSACTION			= 1U << 17,
> >   	PERF_SAMPLE_REGS_INTR			= 1U << 18,
> >   	PERF_SAMPLE_PHYS_ADDR			= 1U << 19,
> > +	PERF_SAMPLE_LBR_TOS			= 1U << 20,
> >   
> > -	PERF_SAMPLE_MAX = 1U << 20,		/* non-ABI */
> > +	PERF_SAMPLE_MAX = 1U << 21,		/* non-ABI */
> >   
> >   	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63, /* non-ABI; internal use */
> >   };
> > @@ -864,6 +865,7 @@ enum perf_event_type {
> >   	 *	{ u64			abi; # enum perf_sample_regs_abi
> >   	 *	  u64			regs[weight(mask)]; } && PERF_SAMPLE_REGS_INTR
> >   	 *	{ u64			phys_addr;} && PERF_SAMPLE_PHYS_ADDR
> > +	 *	{ u64			tos;} && PERF_SAMPLE_LBR_TOS
> >   	 * };
> >   	 */
> >   	PERF_RECORD_SAMPLE			= 9,
>
> I have problems with the API.. You're introducing the intel specific LBR
> naming, and adding a whole new sample type vs extending the existing
> BRANCH_STACK (like you really already do with struct perf_branch_stack). >
> So why not add a bit to PERF_SAMPLE_BRANCH_* to request the presence of
> the TOS field in the PERF_SAMPLE_BRANCH_STACK output?

We never store PERF_SAMPLE_BRANCH_* in a sample. The perf tool cannot 
tell if the sample includes TOS field.
There will be a problem when a new perf tool parsing the data generated 
by an old kernel.


Can we rename the new sample type PERF_SAMPLE_BRANCH_STACK_EXTENSION?

{ u64			version;
  u64			tos;} 		&& PERF_SAMPLE_LBR_TOS

If other platforms want to add their extension, we just need to increase 
the version number. Perf tool will check the version before parsing the 
sample.

Thanks,
Kan