From 051f3ca02e46432c0965e8948f00c07d8a2f09c0 Mon Sep 17 00:00:00 2001 From: Suravee Suthikulpanit Date: Thu, 7 Sep 2017 02:20:05 -0500 Subject: sched/topology: Introduce NUMA identity node sched domain On AMD Family17h-based (EPYC) system, a logical NUMA node can contain upto 8 cores (16 threads) with the following topology. ---------------------------- C0 | T0 T1 | || | T0 T1 | C4 --------| || |-------- C1 | T0 T1 | L3 || L3 | T0 T1 | C5 --------| || |-------- C2 | T0 T1 | #0 || #1 | T0 T1 | C6 --------| || |-------- C3 | T0 T1 | || | T0 T1 | C7 ---------------------------- Here, there are 2 last-level (L3) caches per logical NUMA node. A socket can contain upto 4 NUMA nodes, and a system can support upto 2 sockets. With full system configuration, current scheduler creates 4 sched domains: domain0 SMT (span a core) domain1 MC (span a last-level-cache) domain2 NUMA (span a socket: 4 nodes) domain3 NUMA (span a system: 8 nodes) Note that there is no domain to represent cpus spaning a logical NUMA node. With this hierarchy of sched domains, the scheduler does not balance properly in the following cases: Case1: When running 8 tasks, a properly balanced system should schedule a task per logical NUMA node. This is not the case for the current scheduler. Case2: In some cases, threads are scheduled on the same cpu, while other cpus are idle. This results in run-to-run inconsistency. For example: taskset -c 0-7 sysbench --num-threads=8 --test=cpu \ --cpu-max-prime=100000 run Total execution time ranges from 25.1s to 33.5s depending on threads placement, where 25.1s is when all 8 threads are balanced properly on 8 cpus. Introducing NUMA identity node sched domain, which is based on how SRAT/SLIT table define a logical NUMA node. This results in the following hierarchy of sched domains on the same system described above. domain0 SMT (span a core) domain1 MC (span a last-level-cache) domain2 NODE (span a logical NUMA node) domain3 NUMA (span a socket: 4 nodes) domain4 NUMA (span a system: 8 nodes) This fixes the improper load balancing cases mentioned above. Signed-off-by: Suravee Suthikulpanit Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: bp@suse.de Link: http://lkml.kernel.org/r/1504768805-46716-1-git-send-email-suravee.suthikulpanit@amd.com Signed-off-by: Ingo Molnar --- kernel/sched/topology.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) (limited to 'kernel') diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 86e81f06d36b..f51d123f9fe1 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1332,6 +1332,10 @@ void sched_init_numa(void) if (!sched_domains_numa_distance) return; + /* Includes NUMA identity node at level 0. */ + sched_domains_numa_distance[level++] = curr_distance; + sched_domains_numa_levels = level; + /* * O(nr_nodes^2) deduplicating selection sort -- in order to find the * unique distances in the node_distance() table. @@ -1379,8 +1383,7 @@ void sched_init_numa(void) return; /* - * 'level' contains the number of unique distances, excluding the - * identity distance node_distance(i,i). + * 'level' contains the number of unique distances * * The sched_domains_numa_distance[] array includes the actual distance * numbers. @@ -1441,10 +1444,19 @@ void sched_init_numa(void) for (i = 0; sched_domain_topology[i].mask; i++) tl[i] = sched_domain_topology[i]; + /* + * Add the NUMA identity distance, aka single NODE. + */ + tl[i++] = (struct sched_domain_topology_level){ + .mask = sd_numa_mask, + .numa_level = 0, + SD_INIT_NAME(NODE) + }; + /* * .. and append 'j' levels of NUMA goodness. */ - for (j = 0; j < level; i++, j++) { + for (j = 1; j < level; i++, j++) { tl[i] = (struct sched_domain_topology_level){ .mask = sd_numa_mask, .sd_flags = cpu_numa_flags, -- cgit