[patch 0/2] NOHZ vs. profile/oprofile

Martin Schwidefsky
2009-05-28T15:05:16Z

Greetings,
Rob pointed me to a deficiency with the current profile/oprofile
code together with NOHZ. For us this problem crept in with the
conversion of s390 to generic clock events, git commit 5a62b192
If the system is running with the HZ-tick disabled and the cpu spents
time in idle we see skewed percentages e.g. with the oprofile output.
On an I/O bound system the number of idle ticks is way to small. The
reason is that the generic clock events code reports either zero or
one tick to profile/oprofile on wakeup from idle even if the cpu has
slept much longer.
I've tried to fix that with the two patches in this series and
another pure s390 specific fix (profile_tick is called from
clock_comparator_work which is nonsense). These three do correct the
oprofile output on s390. The best idea I had to get oprofile in good
shape again is to let the system tick at the HZ rate while oprofile
is working. Better ideas welcome.