From: Kim Phillips kim.phillips@amd.com
commit 80cc7bb6c104d733bff60ddda09f19139c61507c upstream.
For data collected on machines with front end stalled cycles supported, such as found on modern AMD CPU families, commit 146540fb545b ("perf stat: Always separate stalled cycles per insn") introduces a new line in CSV output with a leading comma that upsets some automated scripts. Scripts have to use "-e ex_ret_instr" to work around this issue, after upgrading to a version of perf with that commit.
We could add "if (have_frontend_stalled && !config->csv_sep)" to the not (total && avg) else clause, to emphasize that CSV users are usually scripts, and are written to do only what is needed, i.e., they wouldn't typically invoke "perf stat" without specifying an explicit event list.
But - let alone CSV output - why should users now tolerate a constant 0-reporting extra line in regular terminal output?:
BEFORE:
$ sudo perf stat --all-cpus -einstructions,cycles -- sleep 1
Performance counter stats for 'system wide':
181,110,981 instructions # 0.58 insn per cycle # 0.00 stalled cycles per insn 309,876,469 cycles
1.002202582 seconds time elapsed
The user would not like to see the now permanent:
"0.00 stalled cycles per insn"
line fixture, as it gives no useful information.
So this patch removes the printing of the zeroed stalled cycles line altogether, almost reverting the very original commit fb4605ba47e7 ("perf stat: Check for frontend stalled for metrics"), which seems like it was written to normalize --metric-only column output of common Intel machines at the time: modern Intel machines have ceased to support the genericised frontend stalled metrics AFAICT.
AFTER:
$ sudo perf stat --all-cpus -einstructions,cycles -- sleep 1
Performance counter stats for 'system wide':
244,071,432 instructions # 0.69 insn per cycle 355,353,490 cycles
1.001862516 seconds time elapsed
Output behaviour when stalled cycles is indeed measured is not affected (BEFORE == AFTER):
$ sudo perf stat --all-cpus -einstructions,cycles,stalled-cycles-frontend -- sleep 1
Performance counter stats for 'system wide':
247,227,799 instructions # 0.63 insn per cycle # 0.26 stalled cycles per insn 394,745,636 cycles 63,194,485 stalled-cycles-frontend # 16.01% frontend cycles idle
1.002079770 seconds time elapsed
Fixes: 146540fb545b ("perf stat: Always separate stalled cycles per insn") Signed-off-by: Kim Phillips kim.phillips@amd.com Acked-by: Andi Kleen ak@linux.intel.com Acked-by: Jiri Olsa jolsa@redhat.com Acked-by: Song Liu songliubraving@fb.com Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Cong Wang xiyou.wangcong@gmail.com Cc: Davidlohr Bueso dave@stgolabs.net Cc: Jin Yao yao.jin@linux.intel.com Cc: Kan Liang kan.liang@linux.intel.com Cc: Mark Rutland mark.rutland@arm.com Cc: Namhyung Kim namhyung@kernel.org Cc: Peter Zijlstra peterz@infradead.org Link: http://lore.kernel.org/lkml/20200207230613.26709-1-kim.phillips@amd.com Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- tools/perf/util/stat-shadow.c | 6 ------ 1 file changed, 6 deletions(-)
--- a/tools/perf/util/stat-shadow.c +++ b/tools/perf/util/stat-shadow.c @@ -18,7 +18,6 @@ * AGGR_NONE: Use matching CPU * AGGR_THREAD: Not supported? */ -static bool have_frontend_stalled;
struct runtime_stat rt_stat; struct stats walltime_nsecs_stats; @@ -144,7 +143,6 @@ void runtime_stat__exit(struct runtime_s
void perf_stat__init_shadow_stats(void) { - have_frontend_stalled = pmu_have_event("cpu", "stalled-cycles-frontend"); runtime_stat__init(&rt_stat); }
@@ -853,10 +851,6 @@ void perf_stat__print_shadow_stats(struc print_metric(config, ctxp, NULL, "%7.2f ", "stalled cycles per insn", ratio); - } else if (have_frontend_stalled) { - out->new_line(config, ctxp); - print_metric(config, ctxp, NULL, "%7.2f ", - "stalled cycles per insn", 0); } } else if (perf_evsel__match(evsel, HARDWARE, HW_BRANCH_MISSES)) { if (runtime_stat_n(st, STAT_BRANCHES, ctx, cpu) != 0)