Bitbake PSI checker

[Ola x Nilsson <ola.x.nilsson@axis.com>]

Hi,

I've been looking into using the pressure stall information awareness of
bitbake but I have some problems getting it to work.  Actually I think
it just doesn't work at all.

Reading the code I find that
runqueue.QunQueueScheduler.exceeds_max_pressure claims to "Monitor the
difference in pressure at least once per second".  But using some
debugprints added to that method I see output like

1670840023.757171 cpu_pressure 0.0 io_pressure 0.0 mem_pressure 0.0
1670840023.758697 cpu_pressure 0.0 io_pressure 0.0 mem_pressure 0.0
1670840023.760158 cpu_pressure 0.0 io_pressure 0.0 mem_pressure 0.0
1670840023.761733 cpu_pressure 0.0 io_pressure 0.0 mem_pressure 0.0
1670840023.959357 cpu_pressure 969.0 io_pressure 16135.0 mem_pressure 0.0
1670840042.384582 cpu_pressure 8978077.0 io_pressure 1353882.0 mem_pressure 20922.0
1670840042.384582 cpu io  pressure exceeded over 18.677629 seconds
1670840042.486946 cpu_pressure 466.0 io_pressure 30792.0 mem_pressure 0.0
1670840042.490340 cpu_pressure 466.0 io_pressure 30792.0 mem_pressure 0.0

where the first column is the value of 'now', and the pressure values
are the calculated deltas.  The 0-pressure values are probably because
this is very early in the run and the time delta is less than 0.01
seconds. 

But there is a time delta of almost 19 seconds between line 5 and 6, and
unsurprisingly the pressure exceeds my max settings of CPU:600000 and
IO:200000.

But the very next check is only 0.1 second later and while the
prev-values wont be updated, the calculated pressure will be used.  This
pressure will be below my settings and a new task will be started.

Am I missing something here?  If the pressure should be monitored each
second, isn't it reasonable to have some sort of tick to update the
pre-values?  And using the pressure delta of intervals of less than a
second also seems to give too low pressure values.

/Ola Nilsson