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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>