From 4b96a29ba891dd59734cb7be80a900fe93aa2d9f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 25 Oct 2012 14:16:47 +0200 Subject: [PATCH] mm: sched: numa: Implement slow start for working set sampling Add a 1 second delay before starting to scan the working set of a task and starting to balance it amongst nodes. [ note that before the constant per task WSS sampling rate patch the initial scan would happen much later still, in effect that patch caused this regression. ] The theory is that short-run tasks benefit very little from NUMA placement: they come and go, and they better stick to the node they were started on. As tasks mature and rebalance to other CPUs and nodes, so does their NUMA placement have to change and so does it start to matter more and more. In practice this change fixes an observable kbuild regression: # [ a perf stat --null --repeat 10 test of ten bzImage builds to /dev/shm ] !NUMA: 45.291088843 seconds time elapsed ( +- 0.40% ) 45.154231752 seconds time elapsed ( +- 0.36% ) +NUMA, no slow start: 46.172308123 seconds time elapsed ( +- 0.30% ) 46.343168745 seconds time elapsed ( +- 0.25% ) +NUMA, 1 sec slow start: 45.224189155 seconds time elapsed ( +- 0.25% ) 45.160866532 seconds time elapsed ( +- 0.17% ) and it also fixes an observable perf bench (hackbench) regression: # perf stat --null --repeat 10 perf bench sched messaging -NUMA: -NUMA: 0.246225691 seconds time elapsed ( +- 1.31% ) +NUMA no slow start: 0.252620063 seconds time elapsed ( +- 1.13% ) +NUMA 1sec delay: 0.248076230 seconds time elapsed ( +- 1.35% ) The implementation is simple and straightforward, most of the patch deals with adding the /proc/sys/kernel/numa_balancing_scan_delay_ms tunable knob. Signed-off-by: Peter Zijlstra Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Cc: Andrea Arcangeli Cc: Rik van Riel [ Wrote the changelog, ran measurements, tuned the default. ] Signed-off-by: Ingo Molnar Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel --- include/linux/sched.h | 1 + kernel/sched/core.c | 2 +- kernel/sched/fair.c | 5 +++++ kernel/sysctl.c | 7 +++++++ 4 files changed, 14 insertions(+), 1 deletion(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 3784195..7d95a23 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2006,6 +2006,7 @@ enum sched_tunable_scaling { }; extern enum sched_tunable_scaling sysctl_sched_tunable_scaling; +extern unsigned int sysctl_numa_balancing_scan_delay; extern unsigned int sysctl_numa_balancing_scan_period_min; extern unsigned int sysctl_numa_balancing_scan_period_max; extern unsigned int sysctl_numa_balancing_scan_size; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index cad0d09..fbfc484 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1543,7 +1543,7 @@ static void __sched_fork(struct task_struct *p) p->node_stamp = 0ULL; p->numa_scan_seq = p->mm ? p->mm->numa_scan_seq : 0; p->numa_migrate_seq = p->mm ? p->mm->numa_scan_seq - 1 : 0; - p->numa_scan_period = sysctl_numa_balancing_scan_period_min; + p->numa_scan_period = sysctl_numa_balancing_scan_delay; p->numa_work.next = &p->numa_work; #endif /* CONFIG_NUMA_BALANCING */ } diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f6e1f25..7727b01 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -788,6 +788,9 @@ unsigned int sysctl_numa_balancing_scan_period_max = 100*16; /* Portion of address space to scan in MB */ unsigned int sysctl_numa_balancing_scan_size = 256; +/* Scan @scan_size MB every @scan_period after an initial @scan_delay in ms */ +unsigned int sysctl_numa_balancing_scan_delay = 1000; + static void task_numa_placement(struct task_struct *p) { int seq = ACCESS_ONCE(p->mm->numa_scan_seq); @@ -929,6 +932,8 @@ void task_tick_numa(struct rq *rq, struct task_struct *curr) period = (u64)curr->numa_scan_period * NSEC_PER_MSEC; if (now - curr->node_stamp > period) { + if (!curr->node_stamp) + curr->numa_scan_period = sysctl_numa_balancing_scan_period_min; curr->node_stamp = now; if (!time_before(jiffies, curr->mm->numa_next_scan)) { diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 7d3a2e0..48a68cc 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -353,6 +353,13 @@ static struct ctl_table kern_table[] = { #endif /* CONFIG_SMP */ #ifdef CONFIG_NUMA_BALANCING { + .procname = "numa_balancing_scan_delay_ms", + .data = &sysctl_numa_balancing_scan_delay, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = proc_dointvec, + }, + { .procname = "numa_balancing_scan_period_min_ms", .data = &sysctl_numa_balancing_scan_period_min, .maxlen = sizeof(unsigned int), -- 2.7.4