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-irog...@google.com/
This change modifies the expression parsing code by:
- getting rid of the "other" parsing and introducing a boolean argument
to say whether ids should be computed or not.
- expressions are changed so that a pair of value and ids are returned.
- when computing the metric value the ids are unused.
- when computing the ids, constant values and smt_on are assigned to
the value.
- If the value is from an event ID then the event is added to the ids
hashmap and the value set to bottom (encoded as NAN).
- Typically operators union IDs for their inputs and set the value to
bottom, however, if the inputs are constant then these are computed and
propagated as the value.
- If the input is constant to certain operators like:
IDS1 if CONST else IDS2
then the result will be either IDS1 or IDS2 depending on CONST (which
may be evaluated from an entire expression), and so IDS1 or IDS2 may
be discarded avoiding events from being programmed.
- The ids at the end of parsing are added to the context.
Signed-off-by: Ian Rogers
---
tools/perf/tests/expr.c | 17 ++
tools/perf/util/expr.c | 9 +-
tools/perf/util/expr.h | 1 -
tools/perf/util/expr.l | 9 -
tools/perf/util/expr.y | 415
5 files changed, 354 insertions(+), 97 deletions(-)
diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
index 1c881bea7fca..5cab5960b257 100644
--- a/tools/perf/tests/expr.c
+++ b/tools/perf/tests/expr.c
@@ -1,6 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
#include "util/debug.h"
#include "util/expr.h"
+#include "util/smt.h"
#include "tests.h"
#include
#include
@@ -132,6 +133,22 @@ int test__expr(struct test *t __maybe_unused, int subtest
__maybe_unused)
TEST_ASSERT_VAL("find ids", hashmap__find(ctx->ids, "EVENT2,param=3/",
(void **)_ptr));
+ /* Only EVENT1 or EVENT2 need be measured depending on the value of
smt_on. */
+ expr__ctx_clear(ctx);
+ TEST_ASSERT_VAL("find ids",
+ expr__find_ids("EVENT1 if #smt_on else EVENT2",
+ NULL, ctx, 0) == 0);
+ TEST_ASSERT_VAL("find ids", hashmap__size(ctx->ids) == 1);
+ TEST_ASSERT_VAL("find ids", hashmap__find(ctx->ids,
+ smt_on() ? "EVENT1" :
"EVENT2",
+ (void **)_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.c b/tools/perf/util/expr.c
index 1adb6cd202e0..28aaa50c6c68 100644
--- a/tools/perf/util/expr.c
+++ b/tools/perf/util/expr.c
@@ -329,10 +329,9 @@ void expr__ctx_free(struct expr_parse_ctx *ctx)
static int
__expr__parse(double *val, struct expr_parse_ctx *ctx, const char *expr,
- int start, int runtime)
+ bool compute_ids, int runtime)
{
struct expr_scanner_ctx scanner_ctx = {
- .start_token = start,
.runtime = runtime,
};
YY_BUFFER_STATE buffer;
@@ -352,7 +351,7 @@ __expr__parse(double *val, struct expr_parse_ctx *ctx,
const char *expr,
expr_set_debug(1, scanner);
#endif
- ret = expr_parse(val, ctx, scanner);
+ ret = expr_parse(val, ctx, compute_ids, scanner);
expr__flush_buffer(buffer, scanner);
expr__delete_buffer(buffer, scanner);
@@ -363,13 +362,13 @@ __expr__parse(double *val, struct expr_parse_ctx *ctx,
const char *expr,
int expr__parse(double *final_val, struct expr_parse_ctx *ctx,
const char *expr, int runtime)
{
- return __expr__parse(final_val, ctx, expr, EXPR_PARSE, runtime) ? -1 :
0;
+ return __expr__parse(final_val, ctx, expr, /*compute_ids=*/false,
runtime) ? -1 : 0;
}
int expr__find_ids(const char *expr, const char *one,
struct expr_parse_ctx *ctx, int runtime)
{
- int ret = __expr__parse(NULL, ctx, expr, EXPR_OTHER, runtime);
+ int ret = __expr__parse(NULL, ctx, expr, /*compute_ids=*/true, runtime);
if (one)
expr__del_id(ctx, one);
diff --git a/tools/perf/util/expr.h b/tools/perf/util/expr.h
index 62d3ae5ddfba..cefeb2c8d85e 100644
--- a/tools/perf/util/expr.h
