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Date: Fri, 18 Jun 2010 12:25:01 +0800
From: "Alex,Shi" <alex.shi@...el.com>
To: linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com,
a.p.zijlstra@...llo.nl
Cc: yanmin.zhang@...el.com, tim.c.chen@...el.com
Subject: Re: [patch] Over schedule issue fixing
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@...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);
> }
>
>
--
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