liblog: benchmark add BM_log_event_overhead_42 for a well known tag
Measure the cost of using a known test event log tag from
system/core/logcat/event.logtags:
42 answer (to life the universe etc|3)
Test: liblog_benchmarks BM_log_event_overhead_42
Bug: 36683634
Change-Id: Ibd4be82bebfcedd381c84e8078cf6d05a636aa98
diff --git a/liblog/tests/liblog_benchmark.cpp b/liblog/tests/liblog_benchmark.cpp
index 3f79552..c4bf959 100644
--- a/liblog/tests/liblog_benchmark.cpp
+++ b/liblog/tests/liblog_benchmark.cpp
@@ -527,11 +527,13 @@
/*
* Measure the time it takes to submit the android event logging call
* using discrete acquisition (StartBenchmarkTiming() -> StopBenchmarkTiming())
- * under light load. Expect this to be a dozen or so syscall periods (40us)
+ * under light load. Expect this to be a long path to logger to convert the
+ * unknown tag (0) into a tagname (less than 200us).
*/
static void BM_log_event_overhead(int iters) {
for (unsigned long long i = 0; i < (unsigned)iters; ++i) {
StartBenchmarkTiming();
+ // log tag number 0 is not known, nor shall it ever be known
__android_log_btwrite(0, EVENT_TYPE_LONG, &i, sizeof(i));
StopBenchmarkTiming();
logd_yield();
@@ -539,6 +541,28 @@
}
BENCHMARK(BM_log_event_overhead);
+/*
+ * Measure the time it takes to submit the android event logging call
+ * using discrete acquisition (StartBenchmarkTiming() -> StopBenchmarkTiming())
+ * under light load with a known logtag. Expect this to be a dozen or so
+ * syscall periods (less than 40us)
+ */
+static void BM_log_event_overhead_42(int iters) {
+ for (unsigned long long i = 0; i < (unsigned)iters; ++i) {
+ StartBenchmarkTiming();
+ // In system/core/logcat/event.logtags:
+ // # These are used for testing, do not modify without updating
+ // # tests/framework-tests/src/android/util/EventLogFunctionalTest.java.
+ // # system/core/liblog/tests/liblog_benchmark.cpp
+ // # system/core/liblog/tests/liblog_test.cpp
+ // 42 answer (to life the universe etc|3)
+ __android_log_btwrite(42, EVENT_TYPE_LONG, &i, sizeof(i));
+ StopBenchmarkTiming();
+ logd_yield();
+ }
+}
+BENCHMARK(BM_log_event_overhead_42);
+
static void BM_log_event_overhead_null(int iters) {
set_log_null();
BM_log_event_overhead(iters);
diff --git a/logcat/event.logtags b/logcat/event.logtags
index 909f8e2..9f05351 100644
--- a/logcat/event.logtags
+++ b/logcat/event.logtags
@@ -36,6 +36,8 @@
# These are used for testing, do not modify without updating
# tests/framework-tests/src/android/util/EventLogFunctionalTest.java.
+# system/core/liblog/tests/liblog_benchmark.cpp
+# system/core/liblog/tests/liblog_test.cpp
42 answer (to life the universe etc|3)
314 pi
2718 e