Re: [PATCH v5 2/5] perf: Add SNOOP_PEER flag to perf mem data struct

[Liang, Kan]

On 4/24/2022 7:43 AM, Leo Yan wrote:
> On Sat, Apr 23, 2022 at 05:53:28AM -0700, Andi Kleen wrote:
> > > Except SNOOPX_FWD means a no modified cache snooping, it also means it's
> > > a cache conherency from *remote* socket.  This is quite different from we
> > > define SNOOPX_PEER, which only snoop from peer CPU or clusters.

The FWD doesn't have to be *remote*. The definition you quoted is just 
for the "L3 Miss", which is indeed a remote forward. But we still have 
cross-core FWD. See Table 19-101.

Actually, X86 uses the PERF_MEM_REMOTE_REMOTE + PERF_MEM_SNOOPX_FWD to 
indicate the remote FWD, not just SNOOPX_FWD.

> > > If no objection, I prefer we could keep the new snoop type SNOOPX_PEER,
> > > this would be easier for us to distinguish the semantics and support the
> > > statistics for SNOOPX_FWD and SNOOPX_PEER separately.
> > >
> > > I overlooked the flag SNOOPX_FWD, thanks a lot for Kan's reminding.
> >
> > Yes seems better to keep using a separate flag if they don't exactly match.

Yes, I agree with Andi. If you still think the existing flag combination 
doesn't match your requirement, a new separate flag should be 
introduced. I'm not familiar with ARM. I think I will leave it to you 
and the maintainer to decide.

Thanks,
Kan