[Haskell-cafe] Need pointer to explain CPU usage

Robin Palotai palotai.robin at gmail.com
Thu May 8 06:56:06 UTC 2014

Erik: I tried -I0 in the mean time, without effect.

By the way it is GHC 7.6.3, flags are -threaded -rtsopts -O2 -caf-all
-auto-all, runtime flags are +RTS -N -I0.
Also, recent runs didn't show the behavior where CPU would go to zero
after serving a request (goes back to 10% immediately after
finishing), but this is a bit flaky.
If I decrease the base tick rate with -V0.01, the CPU usage is lower -
not sure if that is indicative.

2014-05-08 8:35 GMT+02:00 Erik Hesselink <hesselink at gmail.com>:
> Could it be idle time garbage collection [0]? You can try turning it
> off with '+RTS -I0'.
> Erik
> [0] http://www.haskell.org/ghc/docs/7.6.3/html/users_guide/runtime-control.html#idp38498400
> On Wed, May 7, 2014 at 9:43 PM, Robin Palotai <palotai.robin at gmail.com> wrote:
>> Hello List,
>> I have a tiny scotty-based application, which when compiled and
>> started in profiling mode, consumes 10x CPU it does in normal mode.
>> Interestingly, if I fire a request on the app, CPU usage drops to
>> minimal after finishing the request for a while. But after a few
>> minutes it starts consuming 10x CPU again.
>> First I would have suspected scotty, however collecting time profiling
>> info with -p, -P or -Pa doesn't reveal much. That still not rules
>> scotty out however.
>> To make matters worse, I inspect strange time profiling tick count I
>> can't explain - the .prof file says "2 ticks @ 1000 us", while the
>> application was clearly running idle for a good few seconds.
>> Any ideas what am I missing?
>> Thanks,
>> Robin
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