Messages in this thread | | | Date | Wed, 28 Mar 2012 20:39:35 +0200 | From | Andrea Arcangeli <> | Subject | Re: [PATCH 11/39] autonuma: CPU follow memory algorithm |
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Hi,
On Wed, Mar 28, 2012 at 01:26:08PM +0200, Peter Zijlstra wrote: > Right, so can we agree that the only case where they diverge is single > processes that have multiple threads and are bigger than a single node (either > in memory, cputime or both)?
I think it vastly diverges for processes that are smaller than one node too. 1) your numa/sched goes blind with an almost arbitrary home node, 2) your migrate-on-fault will be unable to provide an efficient and steady async background migration.
> I've asked you several times why you care about that one case so much, but > without answer.
If this case wasn't important to you, you wouldn't need to introduce your syscalls.
> I'll grant you that unmodified such processes might do better with your > stuff, however: > > - your stuff assumes there is a fair amount of locality to exploit. > > I'm not seeing how this is true in general, since data partitioning is hard > and for those problems where its possible people tend to already do so, > yielding natural points to add the syscalls.
Later, I plan to detect this and layout interleaved pages automatically so you don't even need to manually set MPOL_INTERLEAVE.
> - your stuff doesn't actually nest, since a guest kernel has no clue as to > what constitutes a node (or if there even is such a thing) it will randomly > move tasks around on the vcpus, with complete disrespect for whatever host > vcpu<->page mappings you set up. > > guest kernels actively scramble whatever relations you're building by > scanning, destroying whatever (temporal) locality you think you might > have found.
This shall work fine, running AutoNUMA in guest and host. qemu just need to create a vtopology for the guest that matches the hardware topology. Hard binds in the guest will also work great (they create node locality too).
A paravirt layer could also hint the host on the vcpu switches to shift the host numa stats across but I didn't thought too much on this possible paravirt numa-sched optimization, it's not mandatory, just an idea.
> Related to this is that all applications that currently use mbind() and > sched_setaffinity() are trivial to convert.
Too bad firefox isn't using mbind yet. My primary target are the 99% of apps out there running on a 24way 2 node system or equivalent and KVM.
I agree converting qemu to the syscalls would be trivial though.
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