Re: [PATCH v4 4/9] libperf: Add libperf_evsel__mmap()

[Rob Herring]

On Wed, Nov 11, 2020 at 6:01 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> On Fri, Nov 06, 2020 at 03:56:11PM -0600, Rob Herring wrote:
> > On Thu, Nov 5, 2020 at 4:41 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> > >
> > > On Thu, Nov 05, 2020 at 10:19:24AM -0600, Rob Herring wrote:
> > >
> > > SNIP
> > >
> > > > > > >
> > > > > > > that maps page for each event, then perf_evsel__read
> > > > > > > could go through the fast code, no?
> > > > > >
> > > > > > No, because we're not self-monitoring (pid == 0 and cpu == -1). With
> > > > > > the following change:
> > > > > >
> > > > > > diff --git a/tools/lib/perf/tests/test-evsel.c
> > > > > > b/tools/lib/perf/tests/test-evsel.c
> > > > > > index eeca8203d73d..1fca9c121f7c 100644
> > > > > > --- a/tools/lib/perf/tests/test-evsel.c
> > > > > > +++ b/tools/lib/perf/tests/test-evsel.c
> > > > > > @@ -17,6 +17,7 @@ static int test_stat_cpu(void)
> > > > > >  {
> > > > > >         struct perf_cpu_map *cpus;
> > > > > >         struct perf_evsel *evsel;
> > > > > > +       struct perf_event_mmap_page *pc;
> > > > > >         struct perf_event_attr attr = {
> > > > > >                 .type   = PERF_TYPE_SOFTWARE,
> > > > > >                 .config = PERF_COUNT_SW_CPU_CLOCK,
> > > > > > @@ -32,6 +33,15 @@ static int test_stat_cpu(void)
> > > > > >         err = perf_evsel__open(evsel, cpus, NULL);
> > > > > >         __T("failed to open evsel", err == 0);
> > > > > >
> > > > > > +       pc = perf_evsel__mmap(evsel, 0);
> > > > > > +       __T("failed to mmap evsel", pc);
> > > > > > +
> > > > > > +#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__)
> > > > > > +       __T("userspace counter access not supported", pc->cap_user_rdpmc);
> > > > > > +       __T("userspace counter access not enabled", pc->index);
> > > > > > +       __T("userspace counter width not set", pc->pmc_width >= 32);
> > > > > > +#endif
> > > > >
> > > > > I'll need to check, I'm surprised this would depend on the way
> > > > > you open the event
> > > >
> > > > Any more thoughts on this?
> > >
> > > sry I got stuck with other stuff.. I tried your change
> > > and pc->cap_user_rdpmc is 0 because the test creates
> > > software event, which does not support that
> >
> > Sigh, yes, of course.
> >
> > > when I change that to:
> > >
> > >         .type   = PERF_TYPE_HARDWARE,
> > >         .config = PERF_COUNT_HW_CPU_CYCLES,
> > >
> > > I don't see any of those warning you added
> >
> > So I've now implemented the per fd mmap. It seems to run and get some
> > data, but for the above case the counts don't look right.
> >
> > cpu0: count = 0x10883, ena = 0xbf42, run = 0xbf42
> > cpu1: count = 0x1bc65, ena = 0xa278, run = 0xa278
> > cpu2: count = 0x1fab2, ena = 0x91ea, run = 0x91ea
> > cpu3: count = 0x23d61, ena = 0x81ac, run = 0x81ac
> > cpu4: count = 0x2936a, ena = 0x7149, run = 0x7149
> > cpu5: count = 0x2cd4e, ena = 0x634f, run = 0x634f
> > cpu6: count = 0x3139f, ena = 0x53e7, run = 0x53e7
> > cpu7: count = 0x35350, ena = 0x4690, run = 0x4690
> >
> > For comparison, this is what I get using the slow path read():
> > cpu0: count = 0x1c40, ena = 0x188b5, run = 0x188b5
> > cpu1: count = 0x18e0, ena = 0x1b8f4, run = 0x1b8f4
> > cpu2: count = 0x745e, ena = 0x1ab9e, run = 0x1ab9e
> > cpu3: count = 0x2416, ena = 0x1a280, run = 0x1a280
> > cpu4: count = 0x19c7, ena = 0x19b00, run = 0x19b00
> > cpu5: count = 0x1737, ena = 0x19262, run = 0x19262
> > cpu6: count = 0x11d0e, ena = 0x18944, run = 0x18944
> > cpu7: count = 0x20dbe, ena = 0x181f4, run = 0x181f4
>
> hum, could you please send/push changes with that test?
> I can try it and check

Here you go:

git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git user-perf-event-v5

Just comment out the mmap parts to get original behavior.

Rob