qsub ncpus and taskset

qsub ncpus and taskset

Bernd Burgstaller's picture
Bernd Burgstaller
Sat, 10/29/2011 - 07:15

Dear MTLers, Is there a way to specify the taskset (sched_affinity) already with qsub? As I understand, qsub's ncpus option allows to request a certain number of cores, but it does not specify which cores. By the time the job starts on a batch node, a taskset command could conflict with other jobs running on that node? (At least if the other jobs requested a particular sched_affinity.) If so, the only way to allocate specific cores (e.g., 10 cores on one CPU) would be to request exclusive access to a batch node, i.e., set ncpus=40? Thanks, Bernd

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Mike Pearce (Intel)'s picture
Mike Pearce (Intel)
Mon, 10/31/2011 - 09:39

Bernd,
You are basically correct - the qsub ncpus only just requests a number of CPUs from the total available on the batch server. There is no coloration between with the number of CPUs requested and what cores they relate too.

As you said you could specify ncpus=40 to get exclusive access to a whole batch server and then use taskset within your qsub job to specify which cores you wish to use. Another alternative is to specify a particular batch server (i.e. acano03 or acano04) - both of these batch node always run in exclusive mode, so even specifying ncpus=1, on one of these servers, will get youthe entire batch node. Only acano02 is currecntly configured to run in shared mode.

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