linux-kernel - Re: [PATCH v9 00/13] Don't compute events that won't be used in a metric.

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Date:   Wed, 29 Sep 2021 07:35:19 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Paul Clarke <pc@...ibm.com>, kajoljain <kjain@...ux.ibm.com>,
        linux-perf-users@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>,
        Sandeep Dasgupta <sdasgup@...gle.com>
Subject: Re: [PATCH v9 00/13] Don't compute events that won't be used in a
 metric.

On Thu, Sep 23, 2021 at 12:46:03AM -0700, 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.
> 
> v9. adds a missing memory allocation failure check in the pmu-metrics
>     test.  A memory allocation failure in union returns NULL. Some
>     parser debug on IDs is removed. "Modify code layout" is broken
>     apart into 3 changes.  "Don't compute unused events" is broken
>     apart into 4 changes with the tests merged into the change that
>     adds the corresponding optimization. This is trying to address
>     feedback from Jiri Olsa <jolsa@...hat.com>.  The unmodified
>     patches have Reviewed-by: Andi Kleen <ak@...ux.intel.com> added,
>     although the overall patch set is largely the same as v8 which was
>     fully reviewed-by.

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka

> 
> v8. rebases, adds an ability to compute metrics with no events and
>     further breaks apart the "Don't compute unused events" part of the
>     change as requested by Jiri Olsa <jolsa@...hat.com>.
> 
> v7. fixes the fix to be in the correct patch.
> 
> v6. rebases and fixes issues raised by Namhyung Kim <namhyung@...nel.org>,
> a memory leak and a function comment.
> 
> v5. uses macros to reduce boiler plate in patch 5/5 as suggested by
> Andi Kleen <ak@...ux.intel.com>.
> 
> v4. reduces references to BOTTOM/NAN in patch 5/5 by using utility
> functions. It improves comments and fixes an unnecessary union in a
> peephole optimization.
> 
> v3. fixes an assignment in patch 2/5. In patch 5/5 additional comments
> are added and useless frees are replaced by asserts. A new peephole
> optimization is added for the case CONST IF expr ELSE CONST, where the
> the constants are identical, as we don't need to evaluate the IF
> condition.
> 
> v2. is a rebase.
> 
> Ian Rogers (13):
>   perf metric: Restructure struct expr_parse_ctx.
>   perf metric: Use NAN for missing event IDs.
>   perf expr: Remove unused headers and inline d_ratio
>   perf expr: Separate token declataion from type
>   perf expr: Use macros for operators
>   perf expr: Move actions to the left.
>   perf metric: Rename expr__find_other.
>   perf metric: Add utilities to work on ids map.
>   perf metric: Allow metrics with no events
>   perf expr: Merge find_ids and regular parsing
>   perf expr: Propagate constants for binary operations
>   perf metric: Don't compute unused events
>   perf metric: Avoid events for an 'if' constant result
> 
>  tools/perf/tests/expr.c       | 160 ++++++++++++-----
>  tools/perf/tests/pmu-events.c |  54 +++---
>  tools/perf/util/expr.c        | 121 +++++++++++--
>  tools/perf/util/expr.h        |  20 ++-
>  tools/perf/util/expr.l        |   9 -
>  tools/perf/util/expr.y        | 325 +++++++++++++++++++++++++---------
>  tools/perf/util/metricgroup.c | 145 ++++++++-------
>  tools/perf/util/stat-shadow.c |  54 +++---
>  8 files changed, 620 insertions(+), 268 deletions(-)
> 
> -- 
> 2.33.0.464.g1972c5931b-goog
>