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Subject: Re: [PATCH v9 00/13] Don't compute events that won't be used in a
 metric.
To:     Ian Rogers <irogers@google.com>,
        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>
CC:     Stephane Eranian <eranian@google.com>,
        Sandeep Dasgupta <sdasgup@google.com>
References: <20210923074616.674826-1-irogers@google.com>
From:   John Garry <john.garry@huawei.com>
Message-ID: <00eb6280-fad0-66c4-b957-a4d27dffd0da@huawei.com>
Date:   Wed, 29 Sep 2021 16:19:00 +0100
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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>