Re: [RFC PATCH v1 0/3] Retirement latency perf stat support

[Liang, Kan]

On 2024-04-25 6:34 p.m., Ian Rogers wrote:
> Support 'R' as a retirement latency modifier on events. When present
> the evsel will fork perf record and perf report commands, parsing the
> perf report output as the count value. The intent is to do something
> similar to Weilin's series:
> https://lore.kernel.org/lkml/20240402214436.1409476-1-weilin.wang@xxxxxxxxx/
> 
> While the 'R' and the retirement latency are Intel specific, in the
> future I can imagine more evsel like commands that require child
> processes. We can make the logic more generic at that point.
>

I think in generic what we want is the weight/latency information of the
event. 'W' is already occupied by the weak group. Maybe 'L' is a more
generic name than 'R'. With the event modifier, perf collects and report
the weight/latency information of the event in a perf stat command.

Not just changing the evsel, I think a proper output is still required.
It's possible that an end user can use it without metrics. E.g.,
perf stat -e cycles,instructions:L
A possible generic output maybe

1,931,099,931	cycles
  801,826,458	instructions	# Avg Weight1 1000
				# Avg Weight2 800
				# Avg Weight3 500

Thanks,
Kan

> The code is untested on hardware that supports retirement latency, and
> with metrics with retirement latency in them. The record is also of
> sleep and various things need tweaking but I think v1 is good enough
> for people to give input.
> 
> The first patch stops opening a dummy event for tool events. I came
> across this while looking into the issue and we can likely just pick
> it first. I kept it in the series for cleanliness sake.
> 
> The code has benefitted greatly from Weilin's work and Namhyung's
> great review input.
> 
> Ian Rogers (3):
>   perf evsel: Don't open tool events
>   perf parse-events: Add a retirement latency modifier
>   perf evsel: Add retirement latency event support
> 
>  tools/perf/util/evsel.c        | 186 ++++++++++++++++++++++++++++++++-
>  tools/perf/util/evsel.h        |   4 +
>  tools/perf/util/parse-events.c |   2 +
>  tools/perf/util/parse-events.h |   1 +
>  tools/perf/util/parse-events.l |   3 +-
>  5 files changed, 192 insertions(+), 4 deletions(-)
>