[erlang-questions] VM using only 2 out of 8 schedulers available

Hi, We just tried moving more load to the node using only two schedulers. The VM is using 100% cpu on the two cores, with a run queue hovering between 50 and 100 processes. There is no change in active schedulers. As far as I can see, the load is now at a point where the schedulers should become active. Is there anything we can do to understand more about why this is not happening? Knut On Thu, Feb 16, 2012 at 10:19 AM, Knut Nesheim <knutin@REDACTED> wrote: > Thanks for a quick reply. > > During the GMT night which is our low point, we see quite low traffic > on each machine with maybe 5% cpu utilization of each of the 8 cores. > This could explain why some schedulers are put as idle. When traffic > picks up, we're using around 25% of each core. > > The problem for us is that when traffic picks up again, the VM did not > start using the idle schedulers again. erlang:statistics(run_queue) > reports that there almost always are processes waiting, with peaks of > around 20 processes in our case. This causes much higher latency than > when using all cores. > > We will try pushing more load to this node to see if it starts using > the idle schedulers. > > Thanks > Knut > > On Thu, Feb 16, 2012 at 8:01 AM, Kenneth Lundin > <kenneth.lundin@REDACTED> wrote: >> What is your real problem except that there is no reported cpu load on some >> of the cores? >> >> When there is low load on the system i.e. when there are too few runnable >> Erlang processes some of the schedulers will automatically be put as idle >> letting the remaining schedulers run all processes. When the load increases >> the idle schedulers will be taken into service again. >> >> Each scheduler normally runs on one processor core. >> >> Can this explain what you have observed? >> >> /Kenneth Erlang/OTP Ericsson >> >> Den 15 feb 2012 17:53 skrev "Knut Nesheim" <knutin@REDACTED>: >>> >>> Dear list, >>> >>> From time to time we see the VM using only some of the available >>> cores. Typically 2 or 4 out of 8 available cores will be busy, while >>> the others are not used at all. From 'top' and 'htop' we see only some >>> cores being used. >>> >>> We are running the halfword emulator on 8 core machines and the VM is >>> correctly reporting the number of schedulers and the underlying >>> topology. The nodes are utilizing roughly 25% of each of the 8 cores >>> during normal operation. >>> >>> This problem appeared again today and we still have the process >>> running if anyone has any ideas for how to debug the issue. >>> >>> We are on Ubuntu 10.04 LTS, 2.6.32-342-ec2, 64bit, R14B04 with the >>> halfword emulator. The only NIF library we are using is jiffy. >>> >>> Regards >>> Knut >>> _______________________________________________ >>> erlang-questions mailing list >>> erlang-questions@REDACTED >>> http://erlang.org/mailman/listinfo/erlang-questions