Messages in this thread | | | Date | Wed, 11 Nov 2020 08:43:31 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH] sched/topology: Warn when NUMA diameter > 2 |
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On Tue, Nov 10, 2020 at 06:43:00PM +0000, Valentin Schneider wrote: > NUMA topologies where the shortest path between some two nodes requires > three or more hops (i.e. diameter > 2) end up being misrepresented in the > scheduler topology structures. > > This is currently detected when booting a kernel with CONFIG_SCHED_DEBUG=y > + sched_debug on the cmdline, although this will only yield a warning about > sched_group spans not matching sched_domain spans: > > ERROR: groups don't span domain->span > > Add an explicit warning for that case, triggered regardless of > CONFIG_SCHED_DEBUG, and decorate it with an appropriate comment. > > The topology described in the comment can be booted up on QEMU by appending > the following to your usual QEMU incantation: > > -smp cores=4 \ > -numa node,cpus=0,nodeid=0 -numa node,cpus=1,nodeid=1, \ > -numa node,cpus=2,nodeid=2, -numa node,cpus=3,nodeid=3, \ > -numa dist,src=0,dst=1,val=20, -numa dist,src=0,dst=2,val=30, \ > -numa dist,src=0,dst=3,val=40, -numa dist,src=1,dst=2,val=20, \ > -numa dist,src=1,dst=3,val=30, -numa dist,src=2,dst=3,val=20 > > A somewhat more realistic topology (6-node mesh) with the same affliction > can be conjured with: > > -smp cores=6 \ > -numa node,cpus=0,nodeid=0 -numa node,cpus=1,nodeid=1, \ > -numa node,cpus=2,nodeid=2, -numa node,cpus=3,nodeid=3, \ > -numa node,cpus=4,nodeid=4, -numa node,cpus=5,nodeid=5, \ > -numa dist,src=0,dst=1,val=20, -numa dist,src=0,dst=2,val=30, \ > -numa dist,src=0,dst=3,val=40, -numa dist,src=0,dst=4,val=30, \ > -numa dist,src=0,dst=5,val=20, \ > -numa dist,src=1,dst=2,val=20, -numa dist,src=1,dst=3,val=30, \ > -numa dist,src=1,dst=4,val=20, -numa dist,src=1,dst=5,val=30, \ > -numa dist,src=2,dst=3,val=20, -numa dist,src=2,dst=4,val=30, \ > -numa dist,src=2,dst=5,val=40, \ > -numa dist,src=3,dst=4,val=20, -numa dist,src=3,dst=5,val=30, \ > -numa dist,src=4,dst=5,val=20 > > Link: https://lore.kernel.org/lkml/jhjtux5edo2.mognet@arm.com > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
-- Mel Gorman SUSE Labs
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