From c200191d4c2c1aa2ffb62a984b756ac1f02dc55c Mon Sep 17 00:00:00 2001 From: Valentin Schneider Date: Mon, 17 Aug 2020 12:29:56 +0100 Subject: [PATCH] sched/topology: Propagate SD_ASYM_CPUCAPACITY upwards We currently set this flag *only* on domains whose topology level exactly match the level where we detect asymmetry (as returned by asym_cpu_capacity_level()). This is rather problematic. Say there are two clusters in the system, one with a lone big CPU and the other with a mix of big and LITTLE CPUs (as is allowed by DynamIQ): DIE [ ] MC [ ][ ] 0 1 2 3 4 L L B B B asym_cpu_capacity_level() will figure out that the MC level is the one where all CPUs can see a CPU of max capacity, and we will thus set SD_ASYM_CPUCAPACITY at MC level for all CPUs. That lone big CPU will degenerate its MC domain, since it would be alone in there, and will end up with just a DIE domain. Since the flag was only set at MC, this CPU ends up not seeing any SD with the flag set, which is broken. Rather than clearing dflags at every topology level, clear it before entering the topology level loop. This will properly propagate upwards flags that are set starting from a certain level. Signed-off-by: Valentin Schneider Signed-off-by: Ingo Molnar Reviewed-by: Quentin Perret Reviewed-by: Dietmar Eggemann Acked-by: Peter Zijlstra Link: https://lore.kernel.org/r/20200817113003.20802-11-valentin.schneider@arm.com --- include/linux/sched/sd_flags.h | 4 +++- kernel/sched/topology.c | 3 +-- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h index ee5cbfc7189f..40ad0d5c32e3 100644 --- a/include/linux/sched/sd_flags.h +++ b/include/linux/sched/sd_flags.h @@ -83,9 +83,11 @@ SD_FLAG(SD_WAKE_AFFINE, SDF_SHARED_CHILD) /* * Domain members have different CPU capacities * + * SHARED_PARENT: Set from the topmost domain down to the first domain where + * asymmetry is detected. * NEEDS_GROUPS: Per-CPU capacity is asymmetric between groups. */ -SD_FLAG(SD_ASYM_CPUCAPACITY, SDF_NEEDS_GROUPS) +SD_FLAG(SD_ASYM_CPUCAPACITY, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS) /* * Domain members share CPU capacity (i.e. SMT) diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index c662c53736e2..f36ed96f3197 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1988,11 +1988,10 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att /* Set up domains for CPUs specified by the cpu_map: */ for_each_cpu(i, cpu_map) { struct sched_domain_topology_level *tl; + int dflags = 0; sd = NULL; for_each_sd_topology(tl) { - int dflags = 0; - if (tl == tl_asym) { dflags |= SD_ASYM_CPUCAPACITY; has_asym = true; -- 2.11.0