> UCL: (Hep) 20 nodes since a month. Second cluster with 60 nodes has been setup.
> There are contradictory numbers from CC and HEP on the number of slots.
> HEP counts 66 slots, CC 120 slots. Half of the slots have very low priority anyway.
Perhaps a little more explanation is in order in case anyone is interested
or just puzzled. The e-Science "Central Computing Cluster" (UCL-CCC)
currently has 30 worker nodes, each with two hyperthreading processors,
giving a total of 120 "job slots".
The HEP farm has 10 nodes, also with dual hyperthreading processors.
However, each node has 8 virtual processors as far as PBS is concerned,
apart from the PBS server, which has 4. We wanted to be able to run
low-priority jobs on all nodes while nothing more urgent was around, but
still let more urgent jobs run immediately when they arise. Thus there is
a "bulk" queue that can run up to 38 jobs, but these are run at a high
"nice" level so jobs on the other queues can effectively push the bulk
queues into the background while they run. Thus the CE advertises 76
"CPUs".
One other question that arises from this, and was briefly discussed on
LCG-ROLLOUT without coming to any firm conclusions, is what SpecInt rating
to advertise for hyperthreading processors, since each job (if the farm is
fully loaded) gets only half a processor. I've taken the rating of a CPU,
halved it and then added a bit, but I'm open to better suggestions.
Cheers,
Ben
--
Dr Ben Waugh Tel. +44 (0)20 7679 3783
Dept of Physics and Astronomy Internal: 33783
University College London
London WC1E 6BT
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