Hey guys
Kuriakose raised some good questions on a 'post code review'
conversation. There are two, somewhat related problems :
(a) the code (pt_cpufreq_dtrace_walk() and pt_cpufreq_dtrace_account())
assume that the value stored in time_accounted during the last interval
belongs to the first aggregate entry we walk when collecting data for
the current interval.
(b) we should *not* return if the dt_state_time is zero. We need to
continue down walk() and do the accounting.
Consider the following transitions:
t-2 t-1 t
|------------------------|-----------------------|
900 | ----------|--------\ |
800 | ----/ | ----\ |
700 |--------/ | ---------|
which generate the following aggregations (speed, residency):
700 2 900 4
800 1 800 1
We have (because of (b)):
walk() account() | walk() account()
700 800 900 | 700 800 900
dt_state_time 2 1 - | 0 1
total_time 2 1 2 | - 0*
dtrace_time 2 3 2 | - 0*
time_accounted 0 0 2 | - 2
But prior to (b) we still had
walk() account() | walk() account()
700 800 900 | 700 800 900
dt_state_time 2 1 - | 0
total_time 2 1 2 | 0 ...
dtrace_time 2 3 3 | 0
time_accounted 0 0 2 | 0**
** cpuidle.c:525
So we're expecting the aggregation to be ordered descendingly by the
residency at each state, which is not true. It's ordered by its keys.
I'm working on a fix for this now.
Thanks,
Rafael
