sched/numa: Stop multiple tasks from moving to the CPU at the same time
authorSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Fri, 21 Sep 2018 17:48:56 +0000 (23:18 +0530)
committerIngo Molnar <mingo@kernel.org>
Tue, 2 Oct 2018 07:42:20 +0000 (09:42 +0200)
Task migration under NUMA balancing can happen in parallel. More than
one task might choose to migrate to the same CPU at the same time. This
can result in:

- During task swap, choosing a task that was not part of the evaluation.
- During task swap, task which just got moved into its preferred node,
  moving to a completely different node.
- During task swap, task failing to move to the preferred node, will have
  to wait an extra interval for the next migrate opportunity.
- During task movement, multiple task movements can cause load imbalance.

This problem is more likely if there are more cores per node or more
nodes in the system.

Use a per run-queue variable to check if NUMA-balance is active on the
run-queue.

Specjbb2005 results (8 warehouses)
Higher bops are better

2 Socket - 2  Node Haswell - X86
JVMS  Prev    Current  %Change
4     200194  203353   1.57797
1     311331  328205   5.41995

2 Socket - 4 Node Power8 - PowerNV
JVMS  Prev    Current  %Change
1     197654  214384   8.46429

2 Socket - 2  Node Power9 - PowerNV
JVMS  Prev    Current  %Change
4     192605  188553   -2.10379
1     213402  196273   -8.02664

4 Socket - 4  Node Power7 - PowerVM
JVMS  Prev     Current  %Change
8     52227.1  57581.2  10.2516
1     102529   103468   0.915838

There is a regression on power 9 box. If we look at the details,
that box has a sudden jump in cache-misses with this patch.
All other parameters seem to be pointing towards NUMA
consolidation.

perf stats 8th warehouse Multi JVM 2 Socket - 2  Node Haswell - X86
Event                     Before          After
cs                        13,345,784      13,941,377
migrations                1,127,820       1,157,323
faults                    374,736         382,175
cache-misses              55,132,054,603  54,993,823,500
sched:sched_move_numa     1,923           2,005
sched:sched_stick_numa    52              14
sched:sched_swap_numa     595             529
migrate:mm_migrate_pages  1,932           1,573

vmstat 8th warehouse Multi JVM 2 Socket - 2  Node Haswell - X86
Event                   Before  After
numa_hint_faults        60605   67099
numa_hint_faults_local  51804   58456
numa_hit                239945  240416
numa_huge_pte_updates   14      18
numa_interleave         60      65
numa_local              239865  240339
numa_other              80      77
numa_pages_migrated     1931    1574
numa_pte_updates        67823   77182

perf stats 8th warehouse Single JVM 2 Socket - 2  Node Haswell - X86
Event                     Before          After
cs                        3,016,467       3,176,453
migrations                37,326          30,238
faults                    115,342         87,869
cache-misses              11,692,155,554  12,544,479,391
sched:sched_move_numa     965             23
sched:sched_stick_numa    8               0
sched:sched_swap_numa     35              6
migrate:mm_migrate_pages  1,168           10

vmstat 8th warehouse Single JVM 2 Socket - 2  Node Haswell - X86
Event                   Before  After
numa_hint_faults        16286   236
numa_hint_faults_local  11863   201
numa_hit                112482  72293
numa_huge_pte_updates   33      0
numa_interleave         20      26
numa_local              112419  72233
numa_other              63      60
numa_pages_migrated     1144    8
numa_pte_updates        32859   0

perf stats 8th warehouse Multi JVM 2 Socket - 2  Node Power9 - PowerNV
Event                     Before       After
cs                        8,629,724    8,478,820
migrations                221,052      171,323
faults                    308,661      307,499
cache-misses              135,574,913  240,353,599
sched:sched_move_numa     147          214
sched:sched_stick_numa    0            0
sched:sched_swap_numa     2            4
migrate:mm_migrate_pages  64           89

vmstat 8th warehouse Multi JVM 2 Socket - 2  Node Power9 - PowerNV
Event                   Before  After
numa_hint_faults        11481   5301
numa_hint_faults_local  10968   4745
numa_hit                89773   92943
numa_huge_pte_updates   0       0
numa_interleave         1116    899
numa_local              89220   92345
numa_other              553     598
numa_pages_migrated     62      88
numa_pte_updates        11694   5505

perf stats 8th warehouse Single JVM 2 Socket - 2  Node Power9 - PowerNV
Event                     Before     After
cs                        2,272,887  2,066,172
migrations                12,206     11,076
faults                    163,704    149,544
cache-misses              4,801,186  10,398,067
sched:sched_move_numa     44         43
sched:sched_stick_numa    0          0
sched:sched_swap_numa     0          0
migrate:mm_migrate_pages  17         6

vmstat 8th warehouse Single JVM 2 Socket - 2  Node Power9 - PowerNV
Event                   Before  After
numa_hint_faults        2261    3552
numa_hint_faults_local  1993    3347
numa_hit                25726   25611
numa_huge_pte_updates   0       0
numa_interleave         239     213
numa_local              25498   25583
numa_other              228     28
numa_pages_migrated     17      6
numa_pte_updates        2266    3535

perf stats 8th warehouse Multi JVM 4 Socket - 4  Node Power7 - PowerVM
Event                     Before           After
cs                        117,980,962      99,358,136
migrations                3,950,220        4,041,607
faults                    736,979          749,653
cache-misses              224,976,072,879  225,562,543,251
sched:sched_move_numa     504              771
sched:sched_stick_numa    50               14
sched:sched_swap_numa     239              204
migrate:mm_migrate_pages  1,260            1,180

vmstat 8th warehouse Multi JVM 4 Socket - 4  Node Power7 - PowerVM
Event                   Before  After
numa_hint_faults        18293   27409
numa_hint_faults_local  11969   20677
numa_hit                240854  239988
numa_huge_pte_updates   0       0
numa_interleave         0       0
numa_local              240851  239983
numa_other              3       5
numa_pages_migrated     1190    1016
numa_pte_updates        18106   27916

perf stats 8th warehouse Single JVM 4 Socket - 4  Node Power7 - PowerVM
Event                     Before          After
cs                        61,053,158      60,899,307
migrations                551,586         544,668
faults                    244,174         270,834
cache-misses              74,326,766,973  74,543,455,635
sched:sched_move_numa     344             735
sched:sched_stick_numa    24              25
sched:sched_swap_numa     140             174
migrate:mm_migrate_pages  568             816

vmstat 8th warehouse Single JVM 4 Socket - 4  Node Power7 - PowerVM
Event                   Before  After
numa_hint_faults        6461    11059
numa_hint_faults_local  2283    4733
numa_hit                35661   41384
numa_huge_pte_updates   0       0
numa_interleave         0       0
numa_local              35661   41383
numa_other              0       1
numa_pages_migrated     568     815
numa_pte_updates        6518    11323

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Jirka Hladky <jhladky@redhat.com>
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>
Link: http://lkml.kernel.org/r/1537552141-27815-2-git-send-email-srikar@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
kernel/sched/fair.c
kernel/sched/sched.h

index f808ddf2a868e7dbfbac8d7bcf5809b876dc51c9..3b0b75de11418d62b8523ac8a186bbd709b3376b 100644 (file)
@@ -1514,6 +1514,21 @@ struct task_numa_env {
 static void task_numa_assign(struct task_numa_env *env,
                             struct task_struct *p, long imp)
 {
+       struct rq *rq = cpu_rq(env->dst_cpu);
+
+       /* Bail out if run-queue part of active NUMA balance. */
+       if (xchg(&rq->numa_migrate_on, 1))
+               return;
+
+       /*
+        * Clear previous best_cpu/rq numa-migrate flag, since task now
+        * found a better CPU to move/swap.
+        */
+       if (env->best_cpu != -1) {
+               rq = cpu_rq(env->best_cpu);
+               WRITE_ONCE(rq->numa_migrate_on, 0);
+       }
+
        if (env->best_task)
                put_task_struct(env->best_task);
        if (p)
@@ -1569,6 +1584,9 @@ static void task_numa_compare(struct task_numa_env *env,
        long moveimp = imp;
        int dist = env->dist;
 
+       if (READ_ONCE(dst_rq->numa_migrate_on))
+               return;
+
        rcu_read_lock();
        cur = task_rcu_dereference(&dst_rq->curr);
        if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
@@ -1710,6 +1728,7 @@ static int task_numa_migrate(struct task_struct *p)
                .best_cpu = -1,
        };
        struct sched_domain *sd;
+       struct rq *best_rq;
        unsigned long taskweight, groupweight;
        int nid, ret, dist;
        long taskimp, groupimp;
@@ -1811,14 +1830,17 @@ static int task_numa_migrate(struct task_struct *p)
         */
        p->numa_scan_period = task_scan_start(p);
 
+       best_rq = cpu_rq(env.best_cpu);
        if (env.best_task == NULL) {
                ret = migrate_task_to(p, env.best_cpu);
+               WRITE_ONCE(best_rq->numa_migrate_on, 0);
                if (ret != 0)
                        trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
                return ret;
        }
 
        ret = migrate_swap(p, env.best_task, env.best_cpu, env.src_cpu);
+       WRITE_ONCE(best_rq->numa_migrate_on, 0);
 
        if (ret != 0)
                trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
index 4a2e8cae63c41111672a898d3955008cd345c69b..0b9161241bdad5d2cade90520bae1ce1cef3c2d4 100644 (file)
@@ -783,6 +783,7 @@ struct rq {
 #ifdef CONFIG_NUMA_BALANCING
        unsigned int            nr_numa_running;
        unsigned int            nr_preferred_running;
+       unsigned int            numa_migrate_on;
 #endif
        #define CPU_LOAD_IDX_MAX 5
        unsigned long           cpu_load[CPU_LOAD_IDX_MAX];