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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>