Messages in this thread | | | Date | Thu, 25 Mar 2004 22:59:08 +0100 | From | Ingo Molnar <> | Subject | Re: [Lse-tech] [patch] sched-domain cleanups, sched-2.6.5-rc2-mm2-A3 |
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* Andi Kleen <ak@suse.de> 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.
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