[erlang-questions] Dirty CPU schedulers stuck at zero utilization

Rickard Green <>
Wed Jan 16 12:35:25 CET 2019


On 2019-01-15 23:11, Jesse Stimpson wrote:
> Behavior of the schedulers appears to have the same issue with 2093 patch.
> 
> But I did notice something new in the msacc output. There is a very 
> brief period, at approx the same time as the normal schedulers usage 
> spikes, where all the dirty cpu schedulers have a significant sleep 
> time. I've included timestamped excerpts below, starting with the 
> increase in dirty cpu sleep, and ending with a "steady state" utilization.
> 

We just released OTP-21.2.3 containing PR-2093.

I don't think PR-2093 cause the spikes. This change does not affect how 
work is moved between normal and dirty schedulers, only prevents the 
"loss" of dirty schedulers.

If a process is scheduled on a dirty scheduler it wont make progress 
until it has executed on a dirty scheduler and vice versa (for normal 
schedulers). This is the same both before and after PR-2093. Since dirty 
schedulers aren't "lost" after PR-2093 progress of such processes will 
happen earlier which of course change the behavior, but that is due to 
the work load.

Regards,
Rickard


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