Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology
Date	2017-04-14 13:40 +0200
Message-ID	<tw7K1-x1-1@gated-at.bofh.it> (permalink)
References	<tvNrX-3KR-5@gated-at.bofh.it> <tvNrX-3KR-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, Apr 13, 2017 at 10:56:08AM -0300, Lauro Ramos Venancio wrote:
> This patch constructs the sched groups from each CPU perspective. So, on
> a 4 nodes machine with ring topology, while nodes 0 and 2 keep the same
> groups as before [(3, 0, 1)(1, 2, 3)], nodes 1 and 3 have new groups
> [(0, 1, 2)(2, 3, 0)]. This allows moving tasks between any node 2-hops
> apart.

Ah,.. so after drawing pictures I see what went wrong; duh :-(

An equivalent patch would be (if for_each_cpu_wrap() were exposed):

@@ -521,11 +588,11 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu)
 	struct cpumask *covered = sched_domains_tmpmask;
 	struct sd_data *sdd = sd->private;
 	struct sched_domain *sibling;
-	int i;
+	int i, wrap;
 
 	cpumask_clear(covered);
 
-	for_each_cpu(i, span) {
+	for_each_cpu_wrap(i, span, cpu, wrap) {
 		struct cpumask *sg_span;
 
 		if (cpumask_test_cpu(i, covered))


We need to start iterating at @cpu, not start at 0 every time.

Thread

[RFC 2/3] sched/topology: fix sched groups on NUMA machines with mesh topology Lauro Ramos Venancio <lvenanci@redhat.com> - 2017-04-13 16:00 +0200
  Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines  with mesh topology Rik van Riel <riel@redhat.com> - 2017-04-13 17:20 +0200
  Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with  mesh topology Peter Zijlstra <peterz@infradead.org> - 2017-04-13 17:50 +0200
    Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with  mesh topology Lauro Venancio <lvenanci@redhat.com> - 2017-04-13 22:30 +0200
      Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with  mesh topology Lauro Venancio <lvenanci@redhat.com> - 2017-04-13 23:10 +0200
        Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines  with mesh topology Rik van Riel <riel@redhat.com> - 2017-04-14 01:40 +0200
          Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with  mesh topology Peter Zijlstra <peterz@infradead.org> - 2017-04-14 12:50 +0200
  Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with  mesh topology Peter Zijlstra <peterz@infradead.org> - 2017-04-14 13:40 +0200
    Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with  mesh topology Peter Zijlstra <peterz@infradead.org> - 2017-04-14 14:30 +0200
    Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with  mesh topology Peter Zijlstra <peterz@infradead.org> - 2017-04-14 19:00 +0200
      Re: [RFC 2/3] sched/topology: fix sched groups on NUMA machines with  mesh topology Lauro Venancio <lvenanci@redhat.com> - 2017-04-17 16:50 +0200

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