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The test has been failing for some time when two separate runs of
perf benchmarks are recorded for cycles events and their counts are
compared, while once the recording was done with option --bpf-counters
and once without it. It is expected that the count of the samples
should be within a certain range, firstly the difference was set to be
within 10%, which was then later raised to 20%. However, the test case
keeps failing on certain architectures as recording the provided
benchmark can produce completely different counts based on the
current load of the system.
Sampling two separate runs on intel-eaglestream-spr-13 of "perf stat
--no-big-num -e cycles -- perf bench sched messaging -g 1 -l 100 -t":
Performance counter stats for 'perf bench sched messaging -g 1 -l 100 -t':
396782898 cycles
0.010051983 seconds time elapsed
0.008664000 seconds user
0.097058000 seconds sys
Performance counter stats for 'perf bench sched messaging -g 1 -l 100 -t':
1431133032 cycles
0.021803714 seconds time elapsed
0.023377000 seconds user
0.349918000 seconds sys
, which is ranging from 400mil to 1400mil samples.
Instead of recording the cycles use instructions event, which provides
more stable values. At the same time change the tested workload to one
of the provided testing workloads by perf that is not based on a
scheduler, which can provide another dependency on the current load.
Sampling instructions event with the new workload provide much more
stable results on intel-eaglestream-spr-13 of "perf stat --no-big-num
-e instructions -- perf test -w brstack":
Performance counter stats for 'perf test -w brstack':
64584494 instructions
0.009173945 seconds time elapsed
0.007262000 seconds user
0.002071000 seconds sys
Performance counter stats for 'perf test -w brstack':
64672669 instructions
0.008888135 seconds time elapsed
0.005018000 seconds user
0.004018000 seconds sys
Signed-off-by: Veronika Molnarova <vmolnaro@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: mpetlan@redhat.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240625092001.10909-1-vmolnaro@redhat.com
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.