linux-kernel - [PATCH v1 09/51] perf pmu-events: Don't '\0' terminate enum values

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Date:   Sun, 19 Feb 2023 01:28:06 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     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>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
        Sandipan Das <sandipan.das@....com>,
        James Clark <james.clark@....com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        John Garry <john.g.garry@...cle.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Eduard Zingerman <eddyz87@...il.com>,
        Suzuki Poulouse <suzuki.poulose@....com>,
        Leo Yan <leo.yan@...aro.org>,
        Florian Fischer <florian.fischer@...q.space>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Jing Zhang <renyu.zj@...ux.alibaba.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        Perry Taylor <perry.taylor@...el.com>,
        Caleb Biggers <caleb.biggers@...el.com>
Cc:     Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>
Subject: [PATCH v1 09/51] perf pmu-events: Don't '\0' terminate enum values

Encoding enums like '1\0' wastes a byte and could be '1' (no '\0'
terminator) if the 0 case is '0', it also removes a branch for
decompressing.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/pmu-events/jevents.py | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
index dc0c56dccb5e..e82dff3a1228 100755
--- a/tools/perf/pmu-events/jevents.py
+++ b/tools/perf/pmu-events/jevents.py
@@ -54,6 +54,8 @@ _json_metric_attributes = [
     'metric_name', 'metric_group', 'metric_expr', 'desc',
     'long_desc', 'unit', 'compat', 'aggr_mode', 'event_grouping'
 ]
+# Attributes that are bools or enum int values, encoded as '0', '1',...
+_json_enum_attributes = ['aggr_mode', 'deprecated', 'event_grouping', 'perpkg']
 
 def removesuffix(s: str, suffix: str) -> str:
   """Remove the suffix from a string
@@ -360,7 +362,10 @@ class JsonEvent:
         # Convert parsed metric expressions into a string. Slashes
         # must be doubled in the file.
         x = x.ToPerfJson().replace('\\', '\\\\')
-      s += f'{x}\\000' if x else '\\000'
+      if attr in _json_enum_attributes:
+        s += x if x else '0'
+      else:
+        s += f'{x}\\000' if x else '\\000'
     return s
 
   def to_c_string(self, metric: bool) -> str:
@@ -690,16 +695,18 @@ static void decompress_event(int offset, struct pmu_event *pe)
 {
 \tconst char *p = &big_c_string[offset];
 """)
-  enum_attributes = ['aggr_mode', 'deprecated', 'event_grouping', 'perpkg']
   for attr in _json_event_attributes:
     _args.output_file.write(f'\n\tpe->{attr} = ')
-    if attr in enum_attributes:
-      _args.output_file.write("(*p == '\\0' ? 0 : *p - '0');\n")
+    if attr in _json_enum_attributes:
+      _args.output_file.write("*p - '0';\n")
     else:
       _args.output_file.write("(*p == '\\0' ? NULL : p);\n")
     if attr == _json_event_attributes[-1]:
       continue
-    _args.output_file.write('\twhile (*p++);')
+    if attr in _json_enum_attributes:
+      _args.output_file.write('\tp++;')
+    else:
+      _args.output_file.write('\twhile (*p++);')
   _args.output_file.write("""}
 
 static void decompress_metric(int offset, struct pmu_metric *pm)
@@ -708,13 +715,16 @@ static void decompress_metric(int offset, struct pmu_metric *pm)
 """)
   for attr in _json_metric_attributes:
     _args.output_file.write(f'\n\tpm->{attr} = ')
-    if attr in enum_attributes:
-      _args.output_file.write("(*p == '\\0' ? 0 : *p - '0');\n")
+    if attr in _json_enum_attributes:
+      _args.output_file.write("*p - '0';\n")
     else:
       _args.output_file.write("(*p == '\\0' ? NULL : p);\n")
     if attr == _json_metric_attributes[-1]:
       continue
-    _args.output_file.write('\twhile (*p++);')
+    if attr in _json_enum_attributes:
+      _args.output_file.write('\tp++;')
+    else:
+      _args.output_file.write('\twhile (*p++);')
   _args.output_file.write("""}
 
 int pmu_events_table_for_each_event(const struct pmu_events_table *table,
-- 
2.39.2.637.g21b0678d19-goog