[Haskell-cafe] Substantial (1:10??) system dependencies of runtime performance??

[Nick Rudnick]

Dear all,

for quite a while now, I have experienced this issue with some curiosity;
yesterday I had it again, when a program that took well over one hour
before only needed about ten minutes, after a system reboot (recent Ubuntu)
and with no browser started -- finally deciding to post this.

I still can't reproduce these effects, but there is indication it is
connected with browser use (mostly Google Chrome, with usually 10's of
windows and ~100 folders open) and especially use of video players; closing
or killing doesn't seem to set free resources, a reboot or at least suspend
to disk seems to be necessary (suspend to RAM doesn't seem enough).

Roughly, I would say the differences in runtime can reach a factor as much
as 1:10 at many times -- and so I am curious whether this subject has
already been observed or even better discussed elsewhere. I have spoken to
somebody, and our only plausible conclusion was that software like web
browsers is able to somewhat aggressively claim system resources higher in
the privilege hierarchy (cache?? register??), so that they are not
available to other programs any more.

I hope this is interesting to others, too, I guess it is an issue for
anybody programming computation intensive code to be run on standard
systems with other applications running there, too, and having to predict
the estimated runtime to the client.

Maybe I have overseen some libs which are already able to scan the system
state in this regard, or even tell Haskell to behave 'less nice' when other
applications are known to be of lower priority??

Thanks a lot in advance, Nick
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