Messages in this thread | | | Date | Tue, 9 Apr 2024 14:50:21 -0400 | Subject | Re: [PATCH v1] perf stat: Remove evlist__add_default_attrs use strings | From | "Liang, Kan" <> |
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On 2024-04-09 12:04 p.m., Ian Rogers wrote: > On Tue, Apr 9, 2024 at 9:00 AM Liang, Kan <kan.liang@linux.intel.com> wrote: >> >> >> >> On 2024-04-09 11:20 a.m., Ian Rogers wrote: >>>>> + ret = parse_events(evlist, >>>>> + "context-switches," >>>>> + "cpu-migrations," >>>>> + "page-faults," >>>>> + "instructions," >>>>> + "cycles," >>>> "cycles", >>>> "instructions", >>>> >>>> It's better to keep the original order. >>> So the original order was: >>> "cycles," >>> "stalled-cycles-frontend," >>> "stalled-cycles-backend," >>> "instructions" >>> >> >> Right. The stalled-* events are added between default_attrs0 and >> default_attrs1. >> >> >>> but many/most/all core PMUs don't provide the stalled-* events. At the >>> programmer level instructions is the most fundamental thing, so having >>> it last felt wrong hence moving it to be the first after the software >>> events. My thought was, if we're going to reorder things then let's >>> not do a half measure like: >>> "cycles," >>> "instructions," >>> "stalled-cycles-frontend," >>> "stalled-cycles-backend" >>> >>> let's just put things into their best order. It is obviously easy to >>> change but having this way wasn't an accident. There's obviously >>> subjectivity about whether cycles is more fundamental than >>> instructions, my thought is that you get taught instructions first and >>> that these take some number of cycles to execute, hence thinking >>> instructions should have some priority in the output over cycles - >>> some people may not even know what cycles means, it is hard enough >>> when you do given the variety of different clocks 🙂 >>> >> >> My concern is that there may be someone who still relies on the std >> output of perf stat default. So the output format/order matters for >> them. Their scripts probably be broken if the order is changed. > > I think making everyone suffer for the case of a tool that may behave > in this way doesn't make sense. The tool should transition to not care > or to say the json output, or at least contribute a test. There is > precedent for this attitude, the default metrics for topdown removed > the event names in perf stat default output - no one screamed, and I > expect that to be the case here. >
They did, but that happened after the change was merged. And there was no test case for the output at that time.
I agree that if the order is important, there should be a test for it. I've emailed the tool owners I know and see if the change impacts them. But they are all out of office this week and should be back next week. I will let you know regarding their feedback. If the order is important, I will update the stat+std_output.sh.
Thanks, Kan
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