On Mon, Aug 21, 2017 at 06:59:28PM +0100, Brendan Jackman wrote: > Hi Josef, > > Thanks for taking a look. > > On Mon, Aug 21 2017 at 17:26, Josef Bacik wrote: > > On Mon, Aug 21, 2017 at 04:21:28PM +0100, Brendan Jackman wrote: > [...] > >> - local_group = cpumask_test_cpu(this_cpu, > >> - sched_group_span(group)); > >> - > > > > This isn't right is it? cpu isn't necessarily in the very first group of a > > sd > > right? > > I think it is - I haven't grokked the sd/sg setup code in > kernel/sched/topology.c but there is a comment[1] that I interpret as > saying this. I'll take a more careful look tomorrow. > > [1] > http://elixir.free-electrons.com/linux/v4.13-rc6/source/kernel/sched/topology.c#L786 > > If I'm wrong, this can be rewritten not to use that assumption - I did > it this way in the caller ("else if (group == sd->groups)") because I > didn't want to use cpumask_test_cpu, and then changed it inside > find_idlest_group so there weren't two ways of doing the same thing in > the same neighbourhood of code.
No you are quite correct. The sched_domain of a CPU always includes that CPU and the first group of a sched_domain is it's child domain and therefore also includes that CPU.