Messages in this thread Patches in this message | ![/](/images/icornerl.gif) | | Date | Thu, 09 Jan 2003 15:54:08 -0800 | From | "Martin J. Bligh" <> | Subject | Minature NUMA scheduler |
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I tried a small experiment today - did a simple restriction of the O(1) scheduler to only balance inside a node. Coupled with the small initial load balancing patch floating around, this covers 95% of cases, is a trivial change (3 lines), performs just as well as Erich's patch on a kernel compile, and actually better on schedbench.
This is NOT meant to be a replacement for the code Erich wrote, it's meant to be a simple way to get integration and acceptance. Code that just forks and never execs will stay on one node - but we can take the code Erich wrote, and put it in seperate rebalancer that fires much less often to do a cross-node rebalance. All that would be under #ifdef CONFIG_NUMA, the only thing that would touch mainline is these three lines of change, and it's trivial to see they're completely equivalent to the current code on non-NUMA systems.
I also believe that this is the more correct approach in design, it should result in much less cross-node migration of tasks, and less scanning of remote runqueues.
Opinions / comments?
M.
Kernbench: Elapsed User System CPU 2.5.54-mjb3 19.41s 186.38s 39.624s 1191.4% 2.5.54-mjb3-mjbsched 19.508s 186.356s 39.888s 1164.6%
Schedbench 4: AvgUser Elapsed TotalUser TotalSys 2.5.54-mjb3 0.00 35.14 88.82 0.64 2.5.54-mjb3-mjbsched 0.00 31.84 88.91 0.49
Schedbench 8: AvgUser Elapsed TotalUser TotalSys 2.5.54-mjb3 0.00 47.55 269.36 1.48 2.5.54-mjb3-mjbsched 0.00 41.01 252.34 1.07
Schedbench 16: AvgUser Elapsed TotalUser TotalSys 2.5.54-mjb3 0.00 76.53 957.48 4.17 2.5.54-mjb3-mjbsched 0.00 69.01 792.71 2.74
Schedbench 32: AvgUser Elapsed TotalUser TotalSys 2.5.54-mjb3 0.00 145.20 1993.97 11.05 2.5.54-mjb3-mjbsched 0.00 117.47 1798.93 5.95
Schedbench 64: AvgUser Elapsed TotalUser TotalSys 2.5.54-mjb3 0.00 307.80 4643.55 20.36 2.5.54-mjb3-mjbsched 0.00 241.04 3589.55 12.74
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diff -purN -X /home/mbligh/.diff.exclude virgin/kernel/sched.c mjbsched/kernel/sched.c --- virgin/kernel/sched.c Mon Dec 9 18:46:15 2002 +++ mjbsched/kernel/sched.c Thu Jan 9 14:09:17 2003 @@ -654,7 +654,7 @@ static inline unsigned int double_lock_b /* * find_busiest_queue - find the busiest runqueue. */ -static inline runqueue_t *find_busiest_queue(runqueue_t *this_rq, int this_cpu, int idle, int *imbalance) +static inline runqueue_t *find_busiest_queue(runqueue_t *this_rq, int this_cpu, int idle, int *imbalance, unsigned long cpumask) { int nr_running, load, max_load, i; runqueue_t *busiest, *rq_src; @@ -689,7 +689,7 @@ static inline runqueue_t *find_busiest_q busiest = NULL; max_load = 1; for (i = 0; i < NR_CPUS; i++) { - if (!cpu_online(i)) + if (!cpu_online(i) || !((1 << i) & cpumask) ) continue; rq_src = cpu_rq(i); @@ -764,7 +764,8 @@ static void load_balance(runqueue_t *thi struct list_head *head, *curr; task_t *tmp; - busiest = find_busiest_queue(this_rq, this_cpu, idle, &imbalance); + busiest = find_busiest_queue(this_rq, this_cpu, idle, &imbalance, + __node_to_cpu_mask(__cpu_to_node(this_cpu)) ); if (!busiest) goto out; --------------------------------------------------- A tiny change in the current ilb patch is also needed to stop it using a macro from the first patch:
diff -purN -X /home/mbligh/.diff.exclude ilbold/kernel/sched.c ilbnew/kernel/sched.c --- ilbold/kernel/sched.c Thu Jan 9 15:20:53 2003 +++ ilbnew/kernel/sched.c Thu Jan 9 15:27:49 2003 @@ -2213,6 +2213,7 @@ static void sched_migrate_task(task_t *p static int sched_best_cpu(struct task_struct *p) { int i, minload, load, best_cpu, node = 0; + unsigned long cpumask; best_cpu = task_cpu(p); if (cpu_rq(best_cpu)->nr_running <= 2) @@ -2226,9 +2227,11 @@ static int sched_best_cpu(struct task_st node = i; } } + minload = 10000000; - loop_over_node(i,node) { - if (!cpu_online(i)) + cpumask = __node_to_cpu_mask(node); + for (i = 0; i < NR_CPUS; ++i) { + if (!(cpumask & (1 << i))) continue; if (cpu_rq(i)->nr_running < minload) { best_cpu = i;
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