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From:   Ian Rogers <irogers@google.com>
Date:   Wed, 29 Sep 2021 09:09:24 -0700
Message-ID: <CAP-5=fXcq6Npio0n9y8znknNUGJ4ovtbi=hHr4jWG6H38=BzSA@mail.gmail.com>
Subject: Re: [PATCH v9 00/13] Don't compute events that won't be used in a metric.
To:     John Garry <john.garry@huawei.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        Jin Yao <yao.jin@linux.intel.com>, Paul Clarke <pc@us.ibm.com>,
        kajoljain <kjain@linux.ibm.com>,
        linux-perf-users@vger.kernel.org,
        Stephane Eranian <eranian@google.com>,
        Sandeep Dasgupta <sdasgup@google.com>
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On Wed, Sep 29, 2021 at 8:16 AM John Garry <john.garry@huawei.com> wrote:
>
> On 23/09/2021 08:46, Ian Rogers wrote:
> > For a metric like:
> >    EVENT1 if #smt_on else EVENT2
> >
> > currently EVENT1 and EVENT2 will be measured and then when the metric
> > is reported EVENT1 or EVENT2 will be printed depending on the value
> > from smt_on() during the expr parsing. Computing both events is
> > unnecessary and can lead to multiplexing as discussed in this thread:
> > https://lore.kernel.org/lkml/20201110100346.2527031-1-irogers@google.com/
> >
> > This change modifies expression parsing so that constants are
> > considered when building the set of ids (events) and only events not
> > contributing to a constant value are measured.
>
> Based on some testing on my arm64 platform, no regression seen, so:
>
> Tested-by: John Garry <john.garry@huawei.com>

Awesome, much thanks Jiri, John, Andi for the reviews and testing!

Ian