linux-kernel - Re: [PATCH v5 28/34] perf pmus: Split pmus list into core and other

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Date:   Fri, 9 Jun 2023 08:58:49 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Ravi Bangoria <ravi.bangoria@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        John Garry <john.g.garry@...cle.com>,
        Will Deacon <will@...nel.org>,
        James Clark <james.clark@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Jing Zhang <renyu.zj@...ux.alibaba.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Ming Wang <wangming01@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        Sandipan Das <sandipan.das@....com>,
        Dmitrii Dolgov <9erthalion6@...il.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Ali Saidi <alisaidi@...zon.com>, Rob Herring <robh@...nel.org>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Kang Minchul <tegongkang@...il.com>,
        linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v5 28/34] perf pmus: Split pmus list into core and other

On Thu, Jun 08, 2023 at 10:35:02PM -0700, Ian Rogers wrote:
> On Thu, Jun 8, 2023 at 10:30 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
> >
> > On 09-Jun-23 10:10 AM, Ian Rogers wrote:
> > > On Thu, Jun 8, 2023 at 9:01 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
> > >>
> > >> Hi Ian,
> > >
> > > Hi Ravi,
> > >
> > >> On 27-May-23 12:52 PM, Ian Rogers wrote:
> > >>> Split the pmus list into core and other. This will later allow for
> > >>> the core and other pmus to be populated separately.
> > >>>
> > >>> Signed-off-by: Ian Rogers <irogers@...gle.com>
> > >>> Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>
> > >>> ---
> > >>>  tools/perf/util/pmus.c | 52 ++++++++++++++++++++++++++++++------------
> > >>>  1 file changed, 38 insertions(+), 14 deletions(-)
> > >>>
> > >>> diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
> > >>> index 58ff7937e9b7..4ef4fecd335f 100644
> > >>> --- a/tools/perf/util/pmus.c
> > >>> +++ b/tools/perf/util/pmus.c
> > >>> @@ -12,13 +12,19 @@
> > >>>  #include "pmu.h"
> > >>>  #include "print-events.h"
> > >>>
> > >>> -static LIST_HEAD(pmus);
> > >>> +static LIST_HEAD(core_pmus);
> > >>> +static LIST_HEAD(other_pmus);
> > >>
> > >> AMD ibs_fetch// and ibs_op// PMUs are per SMT-thread and are independent of
> > >> core hw pmu. I wonder where does IBS fit. Currently it's part of other_pmus.
> > >> So, is it safe to assume that other_pmus are not just uncore pmus? In that
> > >> case shall we add a comment here?
> > >
> > > I'm a fan of comments. The code has landed in perf-tools-next:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/util/pmus.c?h=perf-tools-next
> > > Do you have any suggestions on wording? I've had limited success
> > > adding glossary terms, for example, offcore vs uncore:
> > > https://perf.wiki.kernel.org/index.php/Glossary#Offcore
> > > I think offcore is a more interconnect related term, but I'd prefer
> > > not to be inventing the definitions. I'd like it if we could be less
> > > ambiguous in the code and provide useful information on the wiki, so
> > > help appreciated :-)
> >
> > Does this look good?
> >
> > /*
> >  * core_pmus:  A PMU belongs to core_pmus if it's name is "cpu" or it's sysfs
> >  *             directory contains "cpus" file. All PMUs belonging to core_pmus
> >  *             must have pmu->is_core=1. If there are more than one PMUs in
> >  *             this list, perf interprets it as a heterogeneous platform.
> 
> 
> Looks good but a nit here. It is heterogeneous from point-of-view of
> PMUs, there are ARM systems where they are heterogenous with big and
> little cores but they have a single homogeneous PMU driver. The perf
> tool will treat them as homogeneous.

For the sake of the comment: there's a little more nuance here.

The intent is that each distinct micro-architecture has its own PMU instance,
but some people write their device trees incorrectly with a single pmu node
rather than separate pmu nodes per micro-architecture.

That should be viewed as a FW bug, even if we have to deal with it here.

Thanks,
Mark.