From 10866e62e8a6907d9072f10f9a0561db0c0cf50b Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 19 Aug 2013 16:57:04 +0200 Subject: [PATCH] sched/fair: Fix the sd_parent_degenerate() code I found that on my WSM box I had a redundant domain: [ 0.949769] CPU0 attaching sched-domain: [ 0.953765] domain 0: span 0,12 level SIBLING [ 0.958335] groups: 0 (cpu_power = 587) 12 (cpu_power = 588) [ 0.964548] domain 1: span 0-5,12-17 level MC [ 0.969206] groups: 0,12 (cpu_power = 1175) 1,13 (cpu_power = 1176) 2,14 (cpu_power = 1176) 3,15 (cpu_power = 1176) 4,16 (cpu_power = 1176) 5,17 (cpu_power = 1176) [ 0.984993] domain 2: span 0-5,12-17 level CPU [ 0.989822] groups: 0-5,12-17 (cpu_power = 7055) [ 0.995049] domain 3: span 0-23 level NUMA [ 0.999620] groups: 0-5,12-17 (cpu_power = 7055) 6-11,18-23 (cpu_power = 7056) Note how domain 2 has only a single group and spans the same CPUs as domain 1. We should not keep such domains and do in fact have code to prune these. It turns out that the 'new' SD_PREFER_SIBLING flag causes this, it makes sd_parent_degenerate() fail on the CPU domain. We can easily fix this by 'ignoring' the SD_PREFER_SIBLING bit and transfering it to whatever domain ends up covering the span. With this patch the domains now look like this: [ 0.950419] CPU0 attaching sched-domain: [ 0.954454] domain 0: span 0,12 level SIBLING [ 0.959039] groups: 0 (cpu_power = 587) 12 (cpu_power = 588) [ 0.965271] domain 1: span 0-5,12-17 level MC [ 0.969936] groups: 0,12 (cpu_power = 1175) 1,13 (cpu_power = 1176) 2,14 (cpu_power = 1176) 3,15 (cpu_power = 1176) 4,16 (cpu_power = 1176) 5,17 (cpu_power = 1176) [ 0.985737] domain 2: span 0-23 level NUMA [ 0.990231] groups: 0-5,12-17 (cpu_power = 7055) 6-11,18-23 (cpu_power = 7056) Reviewed-by: Paul Turner Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-ys201g4jwukj0h8xcamakxq1@git.kernel.org Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index cf8f100433e0..4da0f4bb2ca4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4914,7 +4914,8 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent) SD_BALANCE_FORK | SD_BALANCE_EXEC | SD_SHARE_CPUPOWER | - SD_SHARE_PKG_RESOURCES); + SD_SHARE_PKG_RESOURCES | + SD_PREFER_SIBLING); if (nr_node_ids == 1) pflags &= ~SD_SERIALIZE; } @@ -5118,6 +5119,13 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu) tmp->parent = parent->parent; if (parent->parent) parent->parent->child = tmp; + /* + * Transfer SD_PREFER_SIBLING down in case of a + * degenerate parent; the spans match for this + * so the property transfers. + */ + if (parent->flags & SD_PREFER_SIBLING) + tmp->flags |= SD_PREFER_SIBLING; destroy_sched_domain(parent, cpu); } else tmp = tmp->parent;