Messages in this thread |  | | From | Namhyung Kim <> | Date | Wed, 1 Dec 2021 09:21:52 -0800 | Subject | Re: [RFC/PATCHSET 0/5] perf ftrace: Implement function latency histogram (v1) |
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On Wed, Dec 1, 2021 at 3:59 AM Arnaldo Carvalho de Melo <acme@kernel.org> wrote: > > Em Tue, Nov 30, 2021 at 04:36:49PM -0800, Stephane Eranian escreveu: > > On Tue, Nov 30, 2021 at 2:58 PM Namhyung Kim <namhyung@kernel.org> wrote: > > > On Tue, Nov 30, 2021 at 6:37 AM Arnaldo Carvalho de Melo <acme@kernel.org> wrote: > > > > > Em Mon, Nov 29, 2021 at 03:18:25PM -0800, Namhyung Kim escreveu: > > > > > I've implemented 'latency' subcommand in the perf ftrace command to > > > > > show a histogram of function latency. > > > > > > To handle new subcommands, the existing functionality is moved to > > > > > 'trace' subcommand while preserving backward compatibility of not > > > > > having a subcommand at all (defaults to 'trace'). > > > > > > The latency subcommand accepts a target (kernel, for now) function > > > > > with -T option and shows a histogram like below: > > > > > Humm, wouldn't be interesting to shorten this by having a new 'perf > > > > flat' (function latency) tool, on the same level as 'perf ftrace' and > > > > leave 'perf ftrace' to just being a convenient perf interface to what > > > > ftrace provides? > > > > That would be fine. I also think 'perf ftrace latency' is > > > bit too long. But if we would add a new feature > > > like argdist (in BCC) later, I thought it'd be nice being > > > a subcommand in the perf ftrace together. > > > > But it's up to you. I'll make a change if you prefer > > > 'flat' (or how about 'fnlat' instead?). > > fnlat would be ok, flat was just funny to avoid suggesting it :-)
:)
> > > I am not too fond of the flat option because as we had more bpf tools > > like function latency, then we keep extending the list of commands > > each with a small span which is different > > from what we have right now. > > I think we should focus on the tool end result, not on how it is > implemented, i.e. in this specific "function latency" tool ftrace is > used with BPF, but we could perhaps have used some other mechanism.
Agreed, but I think function latency belongs to function tracing conceptually. So I added it as a subcommand in perf ftrace not just because of the implementation.
> > I think all these tools should have as much as possible a common set of > options, like the targets (cpu, cgroup, pid, tid, etc) so that one can > go from different views for those targets by just changing the name of > the tool.
Currently, perf ftrace shares the target options with both subcommands. Please see common_options in cmd_ftrace().
Thanks, Namhyung
> > We have things like: > > $ perf sched > > Usage: perf sched [<options>] {record|latency|map|replay|script|timehist} > > -D, --dump-raw-trace dump raw trace in ASCII > -f, --force don't complain, do it > -i, --input <file> input file name > -v, --verbose be more verbose (show symbol address, etc) > > With different 3rd level subcommads, but in the 'perf sched' case is the > component being observed, not the mechanism being used to obtain/present > the observation data. > > - Arnaldo
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