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SubjectRe: [RFC/RFT PATCH v3] sched: automated per tty task groups
Peter Zijlstra, le Fri 19 Nov 2010 12:57:24 +0100, a écrit :
> On Fri, 2010-11-19 at 01:07 +0100, Samuel Thibault wrote:
> > Also note that having a hierarchical process structure should permit to
> > make things globally more efficient: avoid putting e.g. your cpp, cc1,
> > and asm processes at three corners of your 4-socket NUMA machine :)
>
> And no, using that to load-balance between CPUs doesn't necessarily help
> with the NUMA case,

It doesn't _necessarily_ help, but it should help in quite a few cases.

> load-balancing is an impossible job (equivalent to
> page-replacement -- you simply don't know the future), applications
> simply do wildly weird stuff.

Sure. Not a reason not to get the low-hanging fruits :)

> From a process hierarchy there's absolutely no difference between a
> cc1/cpp/asm and some MPI jobs, both can be parent-child relations with
> pipes between, some just run short and have data affinity, others run
> long and don't have any.

MPI jobs typically communicate with each other. Keeping them on the same
socket permits to keep shared-memory MPI drivers to mostly remain in
e.g. the L3 cache. That typically gives benefits.

Samuel
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