Messages in this thread |  | | Date | Wed, 8 Aug 2018 09:58:41 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched/topology: Use Identity node only if required |
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On Wed, Aug 08, 2018 at 12:39:31PM +0530, Srikar Dronamraju wrote: > With Commit 051f3ca02e46 ("sched/topology: Introduce NUMA identity node > sched domain") scheduler introduces an extra numa level. However that > leads to > > - numa topology on 2 node systems no more marked as NUMA_DIRECT. After > this commit, it gets reported as NUMA_BACKPLANE. This is because > sched_domains_numa_level now equals 2 on 2 node systems. > > - Extra numa sched domain that gets added and degenerated on most > machines. The Identity node is only needed on very few systems. > Also all non-numa systems will end up populating > sched_domains_numa_distance and sched_domains_numa_masks tables. > > - On shared lpars like powerpc, this extra sched domain creation can > lead to repeated rcu stalls, sometimes even causing unresponsive > systems on boot. On such stalls, it was noticed that > init_sched_groups_capacity() (sg != sd->groups is always true).
The idea was that if the topology level is redundant (as it often is); then the degenerate code would take it out.
Why is that not working (right) and can we fix that instead?
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