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perf metric: Avoid events for an 'if' constant result

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For a metric like:

  CONST if expr else CONST

if the values of CONST are identical then expr doesn't need evaluating,
and events, in order to compute a result.

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: John Garry <john.garry@huawei.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandeep Dasgupta <sdasgup@google.com>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20210923074616.674826-14-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Ian Rogers
2021-09-23 00:46:16 -07:00
committed by Arnaldo Carvalho de Melo
parent a8e4e88083
commit 94886961e3
2 changed files with 17 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
tools/perf/tests/expr.c
View File

@@ -143,6 +143,13 @@ int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
smt_on() ? "EVENT1" : "EVENT2", smt_on() ? "EVENT1" : "EVENT2",
(void **)&val_ptr)); (void **)&val_ptr));
/* The expression is a constant 1.0 without needing to evaluate EVENT1. */
expr__ctx_clear(ctx);
TEST_ASSERT_VAL("find ids",
expr__find_ids("1.0 if EVENT1 > 100.0 else 1.0",
NULL, ctx, 0) == 0);
TEST_ASSERT_VAL("find ids", hashmap__size(ctx->ids) == 0);
expr__ctx_free(ctx); expr__ctx_free(ctx);
return 0; return 0;

10
tools/perf/util/expr.y
View File

@@ -142,6 +142,16 @@ if_expr: expr IF expr ELSE expr
$$.ids = $1.ids; $$.ids = $1.ids;
ids__free($3.ids); ids__free($3.ids);
ids__free($5.ids); ids__free($5.ids);
} else if ($1.val == $5.val) {
/*
* LHS == RHS, so both are an identical constant. No need to
* evaluate any events.
*/
$$.val = $1.val;
$$.ids = NULL;
ids__free($1.ids);
ids__free($3.ids);
ids__free($5.ids);
} else { } else {
/* /*
* Value is either the LHS or RHS and we need the IF expression * Value is either the LHS or RHS and we need the IF expression