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While 'perf sched latency' reports task runtime and delay statistics
(average and maximum delay), it does not provide a visual representation
of how task wait times are distributed across latency ranges between
snapshots (start and finish of the analysis window).
The --histogram option collects CPU wait latencies (time between when
a task becomes runnable and when it gets scheduled onto a CPU) into 22
latency buckets, displaying an ASCII bar chart distribution.
The --hist-mode option configures the bucketing scheme:
- log (default). Logarithmic latency buckets ranging from
sub-microsecond (< 1 us) up to >= 1.05 seconds
- linear. Equal-width linear latency buckets
(i.e., 100 us steps up to >= 2.1 ms)
The --time option allows filtering trace event processing to a
specific time interval [start,stop].
Example histogram output excerpt:
❯ sudo perf sched latency --histogram --CPU 0
CPU Wait Latency Distribution Histogram (between snapshots) (total samples: 36114)
-------------------------------------------------------------------
Latency Range | Count | Pct | Histogram Graph
-------------------------------------------------------------------
< 1 us | 17 | 0.0% | #
2 - 4 us | 673 | 1.9% | #
4 - 8 us | 6237 | 17.3% | ######
8 - 16 us | 3224 | 8.9% | ###
16 - 32 us | 1388 | 3.8% | #
32 - 64 us | 709 | 2.0% | #
64 - 128 us | 690 | 1.9% | #
128 - 256 us | 789 | 2.2% | #
256 - 512 us | 541 | 1.5% | #
512 - 1024 us | 2256 | 6.2% | ##
1 - 2 ms | 3577 | 9.9% | ###
2 - 4 ms | 13259 | 36.7% | ##############
4 - 8 ms | 2523 | 7.0% | ##
8 - 16 ms | 222 | 0.6% | #
16 - 32 ms | 10 | 0.0% | #
>= 1.05 s | 3 | 0.0% | #
-------------------------------------------------------------------
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
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The stop_noploops function will kill the noploop processes that are
running for 10 seconds.
On a loaded machine they may have already terminated meaning the kill
will return an error of no such process.
This doesn't matter and so ignore the error to avoid the test
terminating in the cleanup.
Fixes: 0e22c5ca44e68798 ("perf test: Add sched latency and script shell tests")
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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$ sudo ./perf test -vv 92
92: perf sched tests:
--- start ---
test child forked, pid 1360101
Sched record
pid 1360105's current affinity list: 0-3
pid 1360105's new affinity list: 0
pid 1360107's current affinity list: 0-3
pid 1360107's new affinity list: 0
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 4.330 MB /tmp/__perf_test_sched.perf.data.b3319 (12246 samples) ]
Sched latency
Sched script
Sched map
Sched timehist
Samples of sched_switch event do not have callchains.
---- end(0) ----
92: perf sched tests : Ok
Reviewed-by: Ian Rogers <irogers@google.com>
Tested-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250703014942.1369397-9-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
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Add shell tests covering the `perf sched latency` and `perf sched
script` commands. The test creates 2 noploop processes on the same
forced CPU, it then checks that the process appears in the `perf
sched` output.
Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250628012302.1242532-2-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
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