Re: [PATCHSET 0/4] perf stat: Add --multiply-cgroup option

From: Namhyung Kim
Date: Thu Sep 10 2020 - 22:55:01 EST

Hi Ian,

On Fri, Sep 11, 2020 at 2:11 AM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> Just to throw in some 2c worth. A nice thing about Namhyung's approach
> is that it can apply for metrics, events and pfm-events. It would be
> nice if there were a single option for specifying these, perhaps we
> can figure one out.

Right! Thanks for sharing your opinion. :)

> One thought that came to mind based on Namhyung's multiply name was
> and assuming a cgroup could be a modifier:
> perf record -e cycles:G1
> there could be equivalent to a new syntax of lists and multiplies of:
> perf record -e [cycles]*[:G1]
> This would allow expressions like:
> perf record -e [{instructions,cycles},branches]*[:u,:k]
> which would be equivalent to (showing the effect on sibling groups):
> perf record -e {instructions:u,cycles:u},branches:u,{instructions:k,cycles:k},branches:k
> Adding in cgroups makes a longer list of events:
> perf record -e [{instructions,cycles},branches]*[:u,:k]*[:G1,:G2]
> becomes:
> perf record -e {instructions:u:G1,cycles:u:G1},branches:u:G1,{instructions:k:G1,cycles:k:G1},branches:k:G1,{instructions:u:G2,cycles:u:G2},branches:u:G2,{instructions:k:G2,cycles:k:G2},branches:k:G2
> This is somewhat similar to Arnaldo's proposal but trying to make
> things a bit more generic, avoiding overloading the use of sibling
> groups, .. Perhaps there is a syntax that others prefer or could be
> borrowed from a familiar source like a programming language.

Yes, but this is like a radical change. This would be nice to deal
with repetition in the event list. But I guess mostly we only use a
small number of events (beside the cgroups)...

> I think for Namhyung's sake it is important not to get too distracted
> by desires for better syntax, as this change makes a benefit in a way
> that works with the existing flags. If it is accepted, the man pages
> need to be updated.

Right. I wonder whether they're gonna take the new option
(maybe --for-each-cgroup ?) or not regardless of the syntax change.