Messages in this thread Patch in this message | | | From | Morten Rasmussen <> | Subject | [PATCHv4 12/12] sched/core: Disable SD_PREFER_SIBLING on asymmetric cpu capacity domains | Date | Wed, 4 Jul 2018 11:17:50 +0100 |
| |
The 'prefer sibling' sched_domain flag is intended to encourage spreading tasks to sibling sched_domain to take advantage of more caches and core for SMT systems. It has recently been changed to be on all non-NUMA topology level. However, spreading across domains with cpu capacity asymmetry isn't desirable, e.g. spreading from high capacity to low capacity cpus even if high capacity cpus aren't overutilized might give access to more cache but the cpu will be slower and possibly lead to worse overall throughput.
To prevent this, we need to remove SD_PREFER_SIBLING on the sched_domain level immediately below SD_ASYM_CPUCAPACITY.
cc: Ingo Molnar <mingo@redhat.com> cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> --- kernel/sched/topology.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 29c186961345..00c7a08c7f77 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1140,7 +1140,7 @@ sd_init(struct sched_domain_topology_level *tl, | 0*SD_SHARE_CPUCAPACITY | 0*SD_SHARE_PKG_RESOURCES | 0*SD_SERIALIZE - | 0*SD_PREFER_SIBLING + | 1*SD_PREFER_SIBLING | 0*SD_NUMA | sd_flags , @@ -1186,17 +1186,21 @@ sd_init(struct sched_domain_topology_level *tl, if (sd->flags & SD_ASYM_CPUCAPACITY) { struct sched_domain *t = sd; + /* + * Don't attempt to spread across cpus of different capacities. + */ + if (sd->child) + sd->child->flags &= ~SD_PREFER_SIBLING; + for_each_lower_domain(t) t->flags |= SD_BALANCE_WAKE; } if (sd->flags & SD_SHARE_CPUCAPACITY) { - sd->flags |= SD_PREFER_SIBLING; sd->imbalance_pct = 110; sd->smt_gain = 1178; /* ~15% */ } else if (sd->flags & SD_SHARE_PKG_RESOURCES) { - sd->flags |= SD_PREFER_SIBLING; sd->imbalance_pct = 117; sd->cache_nice_tries = 1; sd->busy_idx = 2; @@ -1207,6 +1211,7 @@ sd_init(struct sched_domain_topology_level *tl, sd->busy_idx = 3; sd->idle_idx = 2; + sd->flags &= ~SD_PREFER_SIBLING; sd->flags |= SD_SERIALIZE; if (sched_domains_numa_distance[tl->numa_level] > RECLAIM_DISTANCE) { sd->flags &= ~(SD_BALANCE_EXEC | @@ -1216,7 +1221,6 @@ sd_init(struct sched_domain_topology_level *tl, #endif } else { - sd->flags |= SD_PREFER_SIBLING; sd->cache_nice_tries = 1; sd->busy_idx = 2; sd->idle_idx = 1; -- 2.7.4
| |