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authorSuravee Suthikulpanit <suravee.suthikulpanit@amd.com>2017-09-07 02:20:05 -0500
committerIngo Molnar <mingo@kernel.org>2017-10-10 11:45:28 +0200
commit051f3ca02e46432c0965e8948f00c07d8a2f09c0 (patch)
treefc238b480b7aeeceb600c1909a9ecedfc50f697e /kernel/sched
parented4ad1ca08a53cf1a805478678d1e7ff0d2cf251 (diff)
downloadlinux-051f3ca02e46432c0965e8948f00c07d8a2f09c0.tar.bz2
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 <suravee.suthikulpanit@amd.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/topology.c18
1 files changed, 15 insertions, 3 deletions
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.
@@ -1442,9 +1445,18 @@ void sched_init_numa(void)
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,