Re: [PATCH] perf arm-spe: Add support for SPE Data Source packet on HiSilicon HIP12

[Leo Yan <leo.yan@arm.com>]

On Tue, Apr 22, 2025 at 08:31:43PM +0800, Yicong Yang wrote:

[...]

> >>> +	case ARM_SPE_HISI_HIP_PEER_CLUSTER:
> >>> +		data_src->mem_lvl = PERF_MEM_LVL_REM_CCE1 | PERF_MEM_LVL_HIT;
> >>> +		data_src->mem_lvl_num = PERF_MEM_LVLNUM_L3;
> > 
> > Seems to me, a CPU has L3 cache, would the cluster has a higher level's
> > cache?
> 
> In my case, the cluster CPUs share the L3 cache and there's several clusters.
> L3's the highest level cache in the system.

If so, you might need to revise the cache levels for:

  ARM_SPE_HISI_HIP_PEER_CPU
  ARM_SPE_HISI_HIP_PEER_CPU_HITM

IIUC, cluster CPUs share L3 cache, and every CPU in a cluster has
L1/L2 cache, for PEER_CPU cases, the memory level should be L2.

[...]

> >>> +	case ARM_SPE_HISI_HIP_REMOTE_SOCKET:
> >>> +		data_src->mem_lvl = PERF_MEM_LVL_REM_CCE2;
> >>> +		data_src->mem_lvl_num = PERF_MEM_LVLNUM_ANY_CACHE;
> >>> +		data_src->mem_remote = PERF_MEM_REMOTE_REMOTE;
> >>> +		data_src->mem_snoopx = PERF_MEM_SNOOPX_PEER;
> >>
> >> Hi Yicong,
> >>
> >> Is the mem_snoop setting missing from this one?
> > 
> > The field 'mem_snoopx' is an extension to the field 'mem_snoop'.
> > 
> > If the field 'mem_snoopx' is set, it is no need to set 'mem_snoop'.
> > 
> 
> they should not be mutal exclusive. mem_snoopx provides the information where
> the cacheline comes from while mem_snoop provides the status of the cacheline.
> if hardware supports we can gather both information from the data source, like
> above for ARM_SPE_HISI_HIP_PEER_CLUSTER_HITM.

My understanding is the PERF_MEM_SNOOPX_PEER flag was extended for
support Arm SPE.  Other snoop flags were original from x86 arch.

I agreed that in some cases above, both the flags PERF_MEM_SNOOPX_PEER
and PERF_MEM_SNOOP_HITM can be set together, you can parse cache sharing
with different --display options:

  perf c2c report --display tot    => based on HITM flags
  perf c2c report --display peer   => based on SNOOPX_PEER flag

> for other cases if there's mem_snoopx information I think mem_snoop can be dropped,
> this won't make differeces. Checked c2c_decode_stats(), only PERF_MEM_SNOOP_HIT and
> PERF_MEM_SNOOP_HITM is useful when summarizing c2c statistics.

It is about how to present accurate results.

E.g., for REMOTE_SOCKET type, it is hard to say the data from remote
DRAM or any level's cache.  Since more hardware details are absent, this
is why I suggested not to set 'mem_snoop' for REMOTE_SOCKET.

Thanks,
Leo