commit f8e58737ebe83853bef263d8fc238af33eebdb33
author Jens Johansen <jensj@google.com> Thu Feb 15 10:30:09 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Feb 15 10:30:09 2024 +0000
tree 2a76bea8f73ccd9c05bc904a46ff19a2939c0649
parent dc586994daaf5d94272d96be29211178ea6f0c2e

[CFE] Add perf event lister tool; more visible warning for benchmarker when scaling is in effect

I do some benchmarking with our benchmarker tool which uses "perf stat"
under the hood.

"perf stat" uses hardware counters, but we have a limited amount of
those. The benchmarker tool asks for 3 event types that will use 3
hardware counters. If there aren't 3 available it will do "scaling" and
only measure what it's asked some percentage of the time so it can still
measure all of the stuff it's asked.

This should be fine. My computer has 4 hardware counters. I think.
Only today I still experienced scaling.
And previously I asked for 4 event types because I had 4 hardware
counters, but then suddenly 1 went missing.

As it turns out another process was using hardware counters.
This CL includes a tool that - at least seeems to - be able to find
other processes using perf events (although it might not be events that
use hardware counters), thus possibly allowing you to kill that or those
process(es). I did, and I now have 4 hardware counters again.

I also made scaling more visible if it happens when using the benchmark
tool. Before it was hidden between other output, not it's also printed
at the end, together with a hint to use the new tool to attempt to fix
it.

Change-Id: Ia51db04a4f25d1d82c3d32b3901cded7d980e7f5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/352525
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>