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From: Niklas Haas <ffmpeg@haasn.xyz>
To: ffmpeg-devel@ffmpeg.org
Date: Mon, 31 Mar 2025 15:30:43 +0200
Message-ID: <20250331133043.167420-1-ffmpeg@haasn.xyz>
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Subject: [FFmpeg-devel] [PATCH] tests/checkasm: increase number of runs in
between measurements
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From: Niklas Haas <git@haasn.dev>
Sometimes, when measuring very small functions, rdtsc is not accurate enough
to get a reliable measurement. This increases the number of runs inside the
inner loop from 4 to 32, which should help a lot. Less important when using
the more precise linux-perf API, but still useful.
There should be no user-visible change since the number of runs is adjusted
to keep the total time spent measuring the same.
---
tests/checkasm/checkasm.h | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)
diff --git a/tests/checkasm/checkasm.h b/tests/checkasm/checkasm.h
index 922e134bfd..b9aac651d7 100644
--- a/tests/checkasm/checkasm.h
+++ b/tests/checkasm/checkasm.h
@@ -340,6 +340,22 @@ typedef struct CheckasmPerf {
#define PERF_STOP(t) t = AV_READ_TIME() - t
#endif
+#define CALL4(...)\
+ do {\
+ tfunc(__VA_ARGS__); \
+ tfunc(__VA_ARGS__); \
+ tfunc(__VA_ARGS__); \
+ tfunc(__VA_ARGS__); \
+ } while (0)
+
+#define CALL16(...)\
+ do {\
+ CALL4(__VA_ARGS__); \
+ CALL4(__VA_ARGS__); \
+ CALL4(__VA_ARGS__); \
+ CALL4(__VA_ARGS__); \
+ } while (0)
+
/* Benchmark the function */
#define bench_new(...)\
do {\
@@ -350,14 +366,12 @@ typedef struct CheckasmPerf {
uint64_t tsum = 0;\
uint64_t ti, tcount = 0;\
uint64_t t = 0; \
- const uint64_t truns = bench_runs;\
+ const uint64_t truns = FFMAX(bench_runs >> 3, 1);\
checkasm_set_signal_handler_state(1);\
for (ti = 0; ti < truns; ti++) {\
PERF_START(t);\
- tfunc(__VA_ARGS__);\
- tfunc(__VA_ARGS__);\
- tfunc(__VA_ARGS__);\
- tfunc(__VA_ARGS__);\
+ CALL16(__VA_ARGS__);\
+ CALL16(__VA_ARGS__);\
PERF_STOP(t);\
if (t*tcount <= tsum*4 && ti > 0) {\
tsum += t;\
--
2.48.1
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