Re: Question about using the perf c2c in UMA system

[Leo Yan <leo.yan@linux.dev>]

On Tue, Apr 30, 2024 at 03:36:02PM +0100, James Clark wrote:

[...]

> >> On Mon, Apr 08, 2024 at 10:52:59AM +0000, ?????? (Baisheng Gao) wrote:
> >>> Hi linux-perf-users,
> >>>
> >>> My perf tool version is 6.6, and I compiled it to run on an Android system.
> >>> The problem is:
> >>>
> >>> # ./perf c2c report
> >>> Failed setup nodes
> >>>
> >>> According to the articles on the Internet, it seems that the perf c2c is only supported
> >>> in NUMA system. However, the cache false sharing does not exist only in NUMA, and
> >>> the UMA system has also the problem. So I wonder how to support perf c2c in UMA.
> >>
> >> The log above is related with parsing NUMA nodes, but this doesn't
> >> mean 'perf c2c' must run on NUMA system. My understanding is both
> >> x86_64 (memory event) and Arm64 (SPE) support 'perf c2c' not only on
> >> NUMA.
> > 
> > The lack of SPE on most ARM hardware really is a pain. Can we add a
> > better error message to make it clearer to users that they need a
> > neoverse CPU? :-)

We cannot stick to Arm Neoverse CPUs as Arm SPE is supported on more CPU
variants. On the other hand, I think we need to dynamically detect CPU
feature for SPE to replace current code for binding specific CPU
variants.

> This issue seems to be about report rather than record, so I'm assuming
> that the record worked and SPE is present.

Yes, this issue is for the report command.

@Baisheng, do you mind to share the steps for reproduce this issue or
drop the perf data file with me? Sorry if I missed your sharing.

> Having said that, the error message for no SPE isn't great, but it's not
> that bad either:
> 
>   $ perf c2c record
>   failed: no PMU supports the memory events

This is better than nothing ;-) I will check a bit for a better log.

Thanks,
Leo