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

Jiri Olsa
2020-09-10T09:16:41Z

On Tue, Sep 08, 2020 at 01:42:24PM +0900, Namhyung Kim wrote:
> Hello,
>
> When we profile cgroup events with perf stat, it's very annoying to
> specify events and cgroups on the command line as it requires the
> mapping between events and cgroups. (Note that perf record can use
> cgroup sampling but it's not usable for perf stat).
>
> I guess most cases we just want to use a same set of events (N) for
> all cgroups (M), but we need to specify NxM events and NxM cgroups.
> This is not good especially when profiling large number of cgroups:
> say M=200.
>
> So I added --multiply-cgroup option to make it easy for that case. It
> will create NxM events from N events and M cgroups. One more upside
> is that it can handle metrics too.

agreed that it's PITA to use -G option ;-)

>
> For example, the following example measures IPC metric for 3 cgroups
>
> $ cat perf-multi-cgrp.sh
> #!/bin/sh
>
> METRIC=${1:-IPC}
> CGROUP_DIR=/sys/fs/cgroup/perf_event
>
> sudo mkdir $CGROUP_DIR/A $CGROUP_DIR/B $CGROUP_DIR/C
>
> # add backgroupd workload for each cgroup
> echo $$ | sudo tee $CGROUP_DIR/A/cgroup.procs > /dev/null
> yes > /dev/null &
> echo $$ | sudo tee $CGROUP_DIR/B/cgroup.procs > /dev/null
> yes > /dev/null &
> echo $$ | sudo tee $CGROUP_DIR/C/cgroup.procs > /dev/null
> yes > /dev/null &
>
> # run 'perf stat' in the root cgroup
> echo $$ | sudo tee $CGROUP_DIR/cgroup.procs > /dev/null
> perf stat -a -M $METRIC --multiply-cgroup -G A,B,C sleep 1

would it be easier to have new option for this? like:

perf stat -a -M $METRIC --for-cgroup A,B,C
perf stat -a -M $METRIC --for-each-cgroup A,B,C
perf stat -a -M $METRIC --attach-cgroup A,B,C
perf stat -a -M $METRIC --attach-to-cgroup A,B,C

I'm still not sure how the --multiply-cgroup deals with empty
cgroup A,,C but looks like we don't need this behaviour now?

thanks,
jirka