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| H A D | perf_cpum_cf.c | diff 9d48c7afedf91a02d03295837ec76b2fb5e7d3fe Wed Nov 03 07:13:04 CDT 2021 Thomas Richter <tmricht@linux.ibm.com> s390/cpumf: cpum_cf PMU displays invalid value after hotplug remove
When a CPU is hotplugged while the perf stat -e cycles command is
running, a wrong (very large) value is displayed immediately after the
CPU removal:
Check the values, shouldn't be too high as in
time counts unit events
1.001101919 29261846 cycles
2.002454499 17523405 cycles
3.003659292 24361161 cycles
4.004816983 18446744073638406144 cycles
5.005671647 <not counted> cycles
...
The CPU hotplug off took place after 3 seconds.
The issue is the read of the event count value after 4 seconds when
the CPU is not available and the read of the counter returns an
error. This is treated as a counter value of zero. This results
in a very large value (0 - previous_value).
Fix this by detecting the hotplugged off CPU and report 0 instead
of a very large number.
Cc: stable@vger.kernel.org
Fixes: a029a4eab39e ("s390/cpumf: Allow concurrent access for CPU Measurement Counter Facility")
Reported-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
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