[PATCH v2] sched/fair: fix update the nohz.next_balance even if we haven't done any load balance

[PATCH v2] sched/fair: fix update the nohz.next_balance even if we haven't done any load balance

[Wanpeng Li]

As Srikar pointed out (https://lkml.org/lkml/2015/3/27/26):

| With the current code when the ilb cpus are not free:
| - We would be updating the nohz.next_balance even through we havent done
|   any load balance.
| - We might iterate thro the nohz.idle_cpus_mask()s to find balance_cpus.

This patch fix it by adding need_resched check with the idle check, and
keep the need_resched check in for loop to catch ilb get busy.

Suggested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Reviewed-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0576ce0..788e42f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7638,7 +7638,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
 	struct rq *rq;
 	int balance_cpu;
 
-	if (idle != CPU_IDLE ||
+	if (idle != CPU_IDLE || need_resched() ||
 	    !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
 		goto end;
 
-- 
1.9.1

Re: [PATCH v2] sched/fair: fix update the nohz.next_balance even if we haven't done any load balance

[Srikar Dronamraju]

* Wanpeng Li <wanpeng.li@linux.intel.com> [2015-03-27 15:52:30]:

> As Srikar pointed out (https://lkml.org/lkml/2015/3/27/26):
> 
> | With the current code when the ilb cpus are not free:
> | - We would be updating the nohz.next_balance even through we havent done
> |   any load balance.
> | - We might iterate thro the nohz.idle_cpus_mask()s to find balance_cpus.
> 
> This patch fix it by adding need_resched check with the idle check, and
> keep the need_resched check in for loop to catch ilb get busy.
> 
> Suggested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Reviewed-by: Jason Low <jason.low2@hp.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>

Looks good to me.

Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0576ce0..788e42f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7638,7 +7638,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
>  	struct rq *rq;
>  	int balance_cpu;
> 
> -	if (idle != CPU_IDLE ||
> +	if (idle != CPU_IDLE || need_resched() ||
>  	    !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
>  		goto end;
> 
> -- 
> 1.9.1
> 

-- 
Thanks and Regards
Srikar Dronamraju