Messages in this thread Patch in this message | | | Date | Sat, 21 Mar 2020 10:37:10 -0700 | Subject | [PATCH v2] perf test x86: address multiplexing in rdpmc test | From | Ian Rogers <> |
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Counters may be being used for pinned or other events which inhibit the instruction counter in the test from being scheduled - time_enabled > 0 but time_running == 0. This causes the test to fail with division by 0. Make time_running an out parameter of mmap_read_self and add a sleep loop to ensure that the counter is running before computing the delta.
v2. Address review feedback from Peter Zijlstra.
Signed-off-by: Ian Rogers <irogers@google.com> --- tools/perf/arch/x86/tests/rdpmc.c | 57 +++++++++++++++++++++++-------- 1 file changed, 42 insertions(+), 15 deletions(-)
diff --git a/tools/perf/arch/x86/tests/rdpmc.c b/tools/perf/arch/x86/tests/rdpmc.c index 1ea916656a2d..64145d4e3d4d 100644 --- a/tools/perf/arch/x86/tests/rdpmc.c +++ b/tools/perf/arch/x86/tests/rdpmc.c @@ -34,20 +34,33 @@ static u64 rdtsc(void) return low | ((u64)high) << 32; } -static u64 mmap_read_self(void *addr) +/* + * Return a user rdpmc result. The kernel may be multiplexing events and so the + * result is scaled to the period of time the counter was enabled. The + * time_running out parameter is set to the amount of time the counter has been + * running. The result will be zero if time_running is zero. + */ +static u64 mmap_read_self(void *addr, u64 *running) { struct perf_event_mmap_page *pc = addr; u32 seq, idx, time_mult = 0, time_shift = 0; - u64 count, cyc = 0, time_offset = 0, enabled, running, delta; + u64 count, cyc = 0, time_offset = 0, enabled, delta; do { seq = pc->lock; barrier(); enabled = pc->time_enabled; - running = pc->time_running; - - if (enabled != running) { + *running = pc->time_running; + + if (*running == 0) { + /* + * Counter won't have a value as due to multiplexing the + * event wasn't scheduled. + */ + return 0; + } + if (enabled != *running) { cyc = rdtsc(); time_mult = pc->time_mult; time_shift = pc->time_shift; @@ -62,7 +75,7 @@ static u64 mmap_read_self(void *addr) barrier(); } while (pc->lock != seq); - if (enabled != running) { + if (enabled != *running) { u64 quot, rem; quot = (cyc >> time_shift); @@ -72,11 +85,11 @@ static u64 mmap_read_self(void *addr) enabled += delta; if (idx) - running += delta; + *running += delta; - quot = count / running; - rem = count % running; - count = quot * enabled + (rem * enabled) / running; + quot = count / *running; + rem = count % *running; + count = quot * enabled + (rem * enabled) / *running; } return count; @@ -104,7 +117,7 @@ static int __test__rdpmc(void) .config = PERF_COUNT_HW_INSTRUCTIONS, .exclude_kernel = 1, }; - u64 delta_sum = 0; + u64 delta_sum = 0, sleep_count = 0; struct sigaction sa; char sbuf[STRERR_BUFSIZE]; @@ -130,14 +143,23 @@ static int __test__rdpmc(void) } for (n = 0; n < 6; n++) { - u64 stamp, now, delta; - - stamp = mmap_read_self(addr); + u64 stamp, now, delta, running; + + for (;;) { + stamp = mmap_read_self(addr, &running); + if (running != 0) + break; + /* Try to wait for event to be running. */ + sleep_count++; + if (sleep_count > 60) + goto out_never_run; + sleep(1); + } for (i = 0; i < loops; i++) tmp++; - now = mmap_read_self(addr); + now = mmap_read_self(addr, &running); loops *= 10; delta = now - stamp; @@ -155,6 +177,11 @@ static int __test__rdpmc(void) return -1; return 0; + +out_never_run: + close(fd); + pr_err("Event counter failed to multiplexed in. Are higher priority counters being sampled by a different process?\n"); + return -1; } int test__rdpmc(struct test *test __maybe_unused, int subtest __maybe_unused) -- 2.25.1.696.g5e7596f4ac-goog
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