Re: [Lse-tech] [patch] sched-domain cleanups, sched-2.6.5-rc2-mm2-A3

From: Andi Kleen (ak_at_suse.de)
Date: 03/25/04

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    Date:	Thu, 25 Mar 2004 16:40:11 +0100
To: "Nakajima, Jun" <jun.nakajima@intel.com>

    On Thu, Mar 25, 2004 at 07:31:37AM -0800, Nakajima, Jun wrote:
    > Andi,
    >
    > Can you be more specific with "it doesn't load balance threads
    > aggressively enough"? Or what behavior of the base NUMA scheduler is
    > missing in the sched-domain scheduler especially for NUMA?

    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.

    -Andi
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