linux-kernel - Re: libperf: lack of interface

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Date:   Tue, 21 Sep 2021 09:46:59 +0000
From:   "nakamura.shun@...itsu.com" <nakamura.shun@...itsu.com>
To:     Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
CC:     Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Rob Herring <robh@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>
Subject: Re: libperf: lack of interface

Hi, Jirka, Arnaldo, and Peter
Sorry for the late reply.

> On Wed, Sep 01, 2021 at 10:36:40AM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Sep 01, 2021 at 09:45:10AM +0000, nakamura.shun@...itsu.com escreveu:
> > > Hello.
> > > 
> > > I'm trying to change rdpmc test in perf_event_tests[1] to use libperf, but libperf doesn't have enough interfaces.
> > > Does anyone plan to implement any of these libperf features?
> > > 
> > > - Interfaces that can run ioctl (PERF_EVENT_IOC_RESET) from userland
> > > - Interfaces that can run fcntl (SIGIO) from userland
> 
> hi,
> we could add perf_evsel__fd like below, would it help your usecase?
> 
> if you described your usecases in more details we could
> see if we could add/move something to libperf for that
> 
> as Arnaldo said below it could be already in tools/perf/util/*.c
> somewhere ;-)

As Peter says, I understood that for rdpmc, no reset is needed.

However, PAPI resets it explicitly, for example, at PAPI_reset.
In other, PAPI also has the ability to call PERF_EVENT_IOC_REFLESH on overflow to call a user-registered handler, using SIGIO.

I think it is desirable to be able to achieve similar functionality.

Best Regards
Shunsuke