Re: [PATCHSET 0/8] perf tools: Do not set attr.exclude_guest by default (v4)

[James Clark]

On 02/10/2024 19:29, Namhyung Kim wrote:
> On Wed, Oct 02, 2024 at 10:49:36AM +0100, James Clark wrote:
> > On 01/10/2024 1:20 am, Namhyung Kim wrote:
> > > Hello,
> > >
> > > I found perf tools set exclude_guest bit inconsistently.  It used to
> > > set the bit but now the default event for perf record doesn't.  So I'm
> > > wondering why we want the bit in the first place.
> > >
> > > Actually it's not good for PMUs don't support any exclusion like AMD
> > > IBS because it disables new features after the exclude_guest due to
> > > the missing feature detection logic.
> > >
> > > v4 changes)
> > >
> > >    * handle EOPNOTSUPP error in compatible way  (Kan)
> > >    * drop --exclude-guest option in perf stat
> > >    * not to separate exclude_hv fallback
> > >    * rename to exclude_GH_default  (Kan)
> > >    * drop the RFC from the subject
> > >
> > > v3) https://lore.kernel.org/lkml/20240905202426.2690105-1-namhyung@xxxxxxxxxx/
> > >
> > >    * move exclude_guest fallback to the front
> > >    * fix precise_max handling on AMD
> > >    * simplify the default event for perf record
> > >
> > > v2) https://lore.kernel.org/lkml/20240904064131.2377873-1-namhyung@xxxxxxxxxx/
> > >
> > >    * update the missing feature detection logic
> > >    * separate exclude_hv fallback
> > >    * add new fallback for exclude_guest
> > >
> > > v1) https://lore.kernel.org/lkml/20240902014621.2002343-1-namhyung@xxxxxxxxxx/
> > >
> > > AFAIK it doesn't matter for the most cases but perf kvm.  If users
> > > need to set the bit, they can still use :H modifier.  For vPMU pass-
> > > through or Apple M1, it'd add the exclude_guest during the fallback
> > > logic.
> > >
> > > Also the kernel feature detection logic should be separated from the
> > > exclude bit tests since it depends on the PMU implementation rather
> > > than the core kernel features.  So I changed it to use a software
> > > event for the detection and factor out some hw-specific checks.
> > >
> > > The code is available at 'perf/exclude-v4' branch in
> > > git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
> > >
> > > Thanks,
> > > Namhyung
> >
> > Looks like you need to allow for :H in the perf stat test on M1 now:
> >
> > diff --git a/tools/perf/tests/shell/stat.sh b/tools/perf/tests/shell/stat.sh
> > index 5a2ca2bcf94d..77cb95859649 100755
> > --- a/tools/perf/tests/shell/stat.sh
> > +++ b/tools/perf/tests/shell/stat.sh
> > @@ -161,7 +161,7 @@ test_hybrid() {
> >     fi
> >
> >     # Run default Perf stat
> > -  cycles_events=$(perf stat -- true 2>&1 | grep -E "/cycles/|  cycles " |
> > wc -l)
> > +  cycles_events=$(perf stat -- true 2>&1 | grep -E "/cycles/|  cycles |  cycles:H  " | wc -l)
>
> Ok, what about "u"?  Probably it can be
>
>    cycles_events=$(perf stat -- true 2>&1 | grep -E "/cycles/(uH)*|  cycles(:[uH])* " | wc -l)

Yep that probably works too and is a bit more robust

> >     if [ "$pmus" -ne "$cycles_events" ]
> >     then
> >
> > Other than that:
> >
> > Reviewed-by: James Clark <james.clark@xxxxxxxxxx>
>
> Thanks for the review!
> Namhyung
>
> > > Namhyung Kim (8):
> > >     perf tools: Add fallback for exclude_guest
> > >     perf tools: Don't set attr.exclude_guest by default
> > >     perf tools: Simplify evsel__add_modifier()
> > >     perf tools: Do not set exclude_guest for precise_ip
> > >     perf tools: Detect missing kernel features properly
> > >     perf tools: Move x86__is_amd_cpu() to util/env.c
> > >     perf tools: Check fallback error and order
> > >     perf record: Just use "cycles:P" as the default event
> > >
> > >    tools/perf/arch/x86/util/Build              |   1 -
> > >    tools/perf/arch/x86/util/env.c              |  19 -
> > >    tools/perf/arch/x86/util/env.h              |   7 -
> > >    tools/perf/arch/x86/util/pmu.c              |   2 +-
> > >    tools/perf/builtin-kvm.c                    |   1 +
> > >    tools/perf/builtin-record.c                 |   4 +-
> > >    tools/perf/builtin-stat.c                   |  18 +-
> > >    tools/perf/dlfilters/dlfilter-test-api-v0.c |   2 +-
> > >    tools/perf/dlfilters/dlfilter-test-api-v2.c |   2 +-
> > >    tools/perf/tests/attr/test-record-dummy-C0  |   2 +-
> > >    tools/perf/tests/parse-events.c             |  30 +-
> > >    tools/perf/util/env.c                       |  24 ++
> > >    tools/perf/util/env.h                       |   4 +
> > >    tools/perf/util/evsel.c                     | 394 ++++++++++++++------
> > >    tools/perf/util/evsel.h                     |   1 -
> > >    tools/perf/util/parse-events.c              |   6 +-
> > >    tools/perf/util/util.c                      |  10 +-
> > >    tools/perf/util/util.h                      |   3 +
> > >    18 files changed, 364 insertions(+), 166 deletions(-)
> > >    delete mode 100644 tools/perf/arch/x86/util/env.c
> > >    delete mode 100644 tools/perf/arch/x86/util/env.h