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authorIan Rogers <[email protected]>2021-09-23 00:46:16 -0700
committerArnaldo Carvalho de Melo <[email protected]>2021-09-29 13:51:04 -0300
commit94886961e324d5b6bae8e206b227c6eeb0f22c2c (patch)
tree0f2b6a404a06e0f5bcadcf6bcb8643cf2bf7cd9f
parenta8e4e880834b5dc53ff6b4cfc9f4268e61399976 (diff)
perf metric: Avoid events for an 'if' constant result
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 <[email protected]> Tested-by: John Garry <[email protected]> Acked-by: Jiri Olsa <[email protected]> Cc: Alexander Shishkin <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Jin Yao <[email protected]> Cc: Kajol Jain <[email protected]> Cc: Mark Rutland <[email protected]> Cc: Namhyung Kim <[email protected]> Cc: Paul Clarke <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Sandeep Dasgupta <[email protected]> Cc: Stephane Eranian <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
-rw-r--r--tools/perf/tests/expr.c7
-rw-r--r--tools/perf/util/expr.y10
2 files changed, 17 insertions, 0 deletions
diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
index 287989321d2a..f1d8411fce12 100644
--- a/tools/perf/tests/expr.c
+++ b/tools/perf/tests/expr.c
@@ -143,6 +143,13 @@ int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
smt_on() ? "EVENT1" : "EVENT2",
(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);
return 0;
diff --git a/tools/perf/util/expr.y b/tools/perf/util/expr.y
index 5b878f044f22..ba7d3b667fcb 100644
--- a/tools/perf/util/expr.y
+++ b/tools/perf/util/expr.y
@@ -142,6 +142,16 @@ if_expr: expr IF expr ELSE expr
$$.ids = $1.ids;
ids__free($3.ids);
ids__free($5.ids);
+ } else if ($1.val == $5.val) {
+ /*
+ * LHS == RHS, so both are an identical constant. No need to
+ * evaluate any events.
+ */
+ $$.val = $1.val;
+ $$.ids = NULL;
+ ids__free($1.ids);
+ ids__free($3.ids);
+ ids__free($5.ids);
} else {
/*
* Value is either the LHS or RHS and we need the IF expression