Using 4 kHz is not necessary and sometimes is more than what was
auto-tuned:
# dmesg | grep max_sample_rate | tail -2
[ 2499.144373] perf interrupt took too long (2501 > 2500), lowering kernel.perf_event_max_sample_rate to 50000
[ 3592.413606] perf interrupt took too long (5069 > 5000), lowering kernel.perf_event_max_sample_rate to 25000
Simulating a auto-tune of 2000 we make the test fail, as reported
by Steven Noonan for one of his machines, so reduce it to 500 HZ,
it is enough to get a good number of samples for this test:
# perf test -v 21 2>&1 | grep '^Reading object code for memory address' | tee /tmp/out | tail -5
Reading object code for memory address: 0x479f40
Reading object code for memory address: 0x7f29b7eea80d
Reading object code for memory address: 0x7f29b7eea80d
Reading object code for memory address: 0x7f29b7eea800
Reading object code for memory address: 0xffffffff813b2f23
[root@jouet ~]# wc -l /tmp/out
40 /tmp/out
[root@jouet ~]#
For systems that auto-tune below that, the previous patches will tell the
user what is happening so that he may either ignore the result of this test or
bump /proc/sys/kernel/perf_event_max_sample_rate.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Noonan <steven@uplinklabs.net>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-6kufyy1iprdfzrbtuqgxir70@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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