Thomas Richter 9d48c7afed 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>
2021-11-08 14:17:49 +01:00
..
2021-10-19 15:39:54 +02:00
2021-08-05 14:10:53 +02:00
2021-11-06 14:48:06 -07:00
2021-07-30 17:09:23 +02:00
2021-07-27 09:39:19 +02:00
2021-10-26 15:21:31 +02:00
2021-09-15 14:29:21 +02:00