Messages in this thread | | | Subject | Re: [patch] Over schedule issue fixing | From | "Alex,Shi" <> | Date | Fri, 18 Jun 2010 12:25:01 +0800 |
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Add Suresh and Peter into thread. Would you like to give some comments of this issue?
Thanks! Alex
On Thu, 2010-06-17 at 14:08 +0800, Alex,Shi wrote: > 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@intel.com> > Signed-off-by: Alex Shi <alex.shi@intel.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); > } > >
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