Re: [PATCH v1 1/8] perf: Increase MAX_NR_CPUS to 4096

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

Hi Ian,

On Fri, Dec 06, 2024 at 08:25:06AM -0800, Ian Rogers wrote:

[...]

> > This series is fine for me.  Just wandering if we can use a central
> > place to maintain the macro, e.g. lib/perf/include/perf/cpumap.h.  It
> > is pointless to define exactly same macros in different headers.  As
> > least, I think we can unify this except the kwork bpf program?
> >
> > P.s. for dynamically allocating per CPU maps in eBPF program, we can
> > refer to the code samples/bpf/xdp_sample_user.c, but this is another
> > topic.
> 
> Thanks Leo,
> 
> can I take this as an acked-by?

Yeah.  I will give my review tags in the cover letter.

> Wrt a single constant I agree,
> following these changes MAX_NR_CPUS is just used for a warning in
> libperf's cpumap.c. I think we're agreed that getting rid of the
> constant would be best. I also think the cpumap logic is duplicating
> something that libc is providing in cpu_set.
>
> And we have more than one representation in perf for the sake of the
> disk representation:

Thanks for sharing the info.

> Just changing the int to be a s16 would lower the memory overhead,
> which is why I'd kind of like the abstraction to be minimal.

Here I am not clear what for "changing the int to be a s16".  Could you
elaberate a bit for this?

Lastly, I also found multiple files use "MAX_CPUS" rather than
"MAX_NR_CPUS".  Polish them in a new series?

Thanks,
Leo