A quick update on this problem which is in my critical path.
I just noticed, in an attempt to reproduce it, that during the package
setup part of the racket compilation procedure the same happens.

I am running `make CPUS=24 in-place`on a 36 cpu machine and I see that
not only sometimes the racket process status goes from 'R' to 'D' (which
also happens in my case), the CPUs are never really working at 100% with
a lot of the work being done at kernel level.

Has anyone ever noticed this?

On 01/10/2018 11:13, 'Paulo Matos' via Racket Users wrote:
> Hi,
> I am not sure this is an issue with places or what it could be but my
> devops-fu is poor and I am not even sure how to debug something like
> this so maybe someone with more knowledge than me on this might chime in
> to hint on a possible debug method.
> I was running some benchmarks and noticed something odd for the first
> time (although it doesn't mean it was ok before, just that this is the
> first time I am actually analysing this issue).
> My program (the master) will create N places (the workers) and each
> place will start by issuing a rosette call which will trigger a call to
> the z3 smt solver. So, N instances of Z3 will run and after it is done
> it will run pure racket code that implements a graph search algorithm.
> This N worker places are actually in a sync call waiting for messages
> from the master and the work is being done by a thread on the worker
> place. The master is either waiting for the timeout to arrive or for a
> solution to be sent from a worker.
> The interesting thing is that when the Z3 instances are running I get
> all my 16 CPUs (on a dedicated machine) working at 100%. When the racket
> code is running the search, they are all holding off at around 60%-80%
> with a huge portion of it in the kernel (red bars in htop).
> Since the Z3 calls come before the threads inside the places are started
> and we get to the sync call, is it possible something bad is happening
> in the sync call that uses the kernel so much? Take a look at htop
> during Z3 and during the search - screenshots attached.
> Are there any suggestions on what the problem might be or how I could
> start to understand why the kernel is so active?
> Kind regards,

Paulo Matos

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