From: Ingo M. <mi...@el...> - 2004-03-25 21:59:09
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* Andi Kleen <ak...@su...> wrote: > It doesn't do load balance in wake_up_forked_process() and is > relatively non aggressive in balancing later. This leads to the > multithreaded OpenMP STREAM running its childs first on the same node > as the original process and allocating memory there. Then later they > run on a different node when the balancing finally happens, but > generate cross traffic to the old node, instead of using the memory > bandwidth of their local nodes. > > The difference is very visible, even the 4 thread STREAM only sees the > bandwidth of a single node. With a more aggressive scheduler you get 4 > times as much. > > Admittedly it's a bit of a stupid benchmark, but seems to > representative for a lot of HPC codes. There's no way the scheduler can figure out the scheduling and memory use patterns of the new tasks in advance. but userspace could give hints - e.g. a syscall that triggers a rebalancing: sys_sched_load_balance(). This way userspace notifies the scheduler that it is on 'zero ground' and that the scheduler can move it to the least loaded cpu/node. a variant of this is already possible, userspace can use setaffinity to load-balance manually - but sched_load_balance() would be automatic. Ingo |