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Date: Thu, 17 Jun 2010 14:08:13 +0800 From: "Alex,Shi" <alex.shi@...el.com> To: linux-kernel@...r.kernel.org Cc: yanmin.zhang@...el.com, tim.c.chen@...el.com Subject: [patch] Over schedule issue fixing commit e709715915d69b6a929d77e7652c9c3fea61c317 introduced an imbalance schedule issue. If we do not use CGROUP, function update_h_load won't want to update h_load. When the system has a large number of tasks far more than logical CPU number, the incorrect cfs_rq[cpu]->h_load value will cause load_balance() to pull too many tasks to local CPU from the busiest CPU. So the busiest CPU keeps being in a round robin. That will hurt performance. The issue was found originally by a scientific calculation workload that developed by Yanmin. with the commit, the workload performance drops about 40% from this commit. We can be reproduced by a short program as following. # gcc -o sl sched-loop.c -lpthread # ./sl -n 100 -t 100 & # cat /proc/sched_debug &> sd1 # grep -A 1 cpu# sd1 sd1:cpu#0, 2533.008 MHz sd1- .nr_running : 2 -- sd1:cpu#1, 2533.008 MHz sd1- .nr_running : 1 -- sd1:cpu#2, 2533.008 MHz sd1- .nr_running : 11 -- sd1:cpu#3, 2533.008 MHz sd1- .nr_running : 12 -- sd1:cpu#4, 2533.008 MHz sd1- .nr_running : 6 -- sd1:cpu#5, 2533.008 MHz sd1- .nr_running : 11 -- sd1:cpu#6, 2533.008 MHz sd1- .nr_running : 10 -- sd1:cpu#7, 2533.008 MHz sd1- .nr_running : 12 -- sd1:cpu#8, 2533.008 MHz sd1- .nr_running : 11 -- sd1:cpu#9, 2533.008 MHz sd1- .nr_running : 12 -- sd1:cpu#10, 2533.008 MHz sd1- .nr_running : 1 -- sd1:cpu#11, 2533.008 MHz sd1- .nr_running : 1 -- sd1:cpu#12, 2533.008 MHz sd1- .nr_running : 6 -- sd1:cpu#13, 2533.008 MHz sd1- .nr_running : 2 -- sd1:cpu#14, 2533.008 MHz sd1- .nr_running : 2 -- sd1:cpu#15, 2533.008 MHz sd1- .nr_running : 1 After apply the fixing patch, cfs_rq get balance. sd1:cpu#0, 2533.479 MHz sd1- .nr_running : 7 -- sd1:cpu#1, 2533.479 MHz sd1- .nr_running : 7 -- sd1:cpu#2, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#3, 2533.479 MHz sd1- .nr_running : 7 -- sd1:cpu#4, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#5, 2533.479 MHz sd1- .nr_running : 7 -- sd1:cpu#6, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#7, 2533.479 MHz sd1- .nr_running : 7 -- sd1:cpu#8, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#9, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#10, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#11, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#12, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#13, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#14, 2533.479 MHz sd1- .nr_running : 6 -- sd1:cpu#15, 2533.479 MHz sd1- .nr_running : 6 --- #include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <pthread.h> volatile int * exiting; void *idle_loop(){ volatile int calc01 = 100; while(*exiting !=1) calc01++; } int main(int argc, char *argv[]){ int i, t, c, er=0, num=8; static char optstr[] = "n:t:"; pthread_t ptid[1024]; while ((c = getopt(argc, argv, optstr)) != EOF) switch (c) { case 'n': num = atoi(optarg); break; case 't': t = atoi(optarg); break; case '?': er = 1; break; } if (er) { printf("usage: %s %s\n", argv[0], optstr); exit(1); } exiting = malloc(sizeof(int)); *exiting = 0; for(i=0; i<num ; i++) pthread_create(&ptid[i], NULL, idle_loop, NULL); sleep(t); *exiting = 1; for (i=0; i<num; i++) pthread_join(ptid[i], NULL); exit(0); } Reviewed-by: Yanmin zhang <yanmin.zhang@...el.com> Signed-off-by: Alex Shi <alex.shi@...el.com> diff --git a/kernel/sched.c b/kernel/sched.c index f8b8996..a18bf93 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1660,9 +1660,6 @@ static void update_shares(struct sched_domain *sd) static void update_h_load(long cpu) { - if (root_task_group_empty()) - return; - walk_tg_tree(tg_load_down, tg_nop, (void *)cpu); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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