linux-kernel - Re: [RFC][PATCH 13/16] sched: Add core wide task selection and scheduling.

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Date:   Tue, 2 Apr 2019 21:20:55 +0800
From:   Aaron Lu <aaron.lwe@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Aaron Lu <aaron.lu@...ux.alibaba.com>, mingo@...nel.org,
        tglx@...utronix.de, pjt@...gle.com, tim.c.chen@...ux.intel.com,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        subhra.mazumdar@...cle.com, fweisbec@...il.com,
        keescook@...omium.org, kerrnel@...gle.com,
        Aubrey Li <aubrey.intel@...il.com>
Subject: Re: [RFC][PATCH 13/16] sched: Add core wide task selection and
 scheduling.

On Tue, Apr 02, 2019 at 10:28:12AM +0200, Peter Zijlstra wrote:
> Another approach would be something like the below:
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -87,7 +87,7 @@ static inline int __task_prio(struct tas
>   */
>  
>  /* real prio, less is less */
> -static inline bool __prio_less(struct task_struct *a, struct task_struct *b, bool runtime)
> +static inline bool __prio_less(struct task_struct *a, struct task_struct *b, u64 vruntime)
>  {
>  	int pa = __task_prio(a), pb = __task_prio(b);
>  
> @@ -104,21 +104,25 @@ static inline bool __prio_less(struct ta
>  	if (pa == -1) /* dl_prio() doesn't work because of stop_class above */
>  		return !dl_time_before(a->dl.deadline, b->dl.deadline);
>  
> -	if (pa == MAX_RT_PRIO + MAX_NICE && runtime) /* fair */
> -		return !((s64)(a->se.vruntime - b->se.vruntime) < 0);
> +	if (pa == MAX_RT_PRIO + MAX_NICE) /* fair */
> +		return !((s64)(a->se.vruntime - vruntime) < 0);
>  
>  	return false;
>  }
>  
>  static inline bool cpu_prio_less(struct task_struct *a, struct task_struct *b)
>  {
> -	return __prio_less(a, b, true);
> +	return __prio_less(a, b, b->se.vruntime);
>  }
>  
>  static inline bool core_prio_less(struct task_struct *a, struct task_struct *b)
>  {
> -	/* cannot compare vruntime across CPUs */
> -	return __prio_less(a, b, false);
> +	u64 vruntime = b->se.vruntime;
> +
> +	vruntime -= task_rq(b)->cfs.min_vruntime;
> +	vruntime += task_rq(a)->cfs.min_vruntime
> +
> +	return __prio_less(a, b, vruntime);
>  }
>  
>  static inline bool __sched_core_less(struct task_struct *a, struct task_struct *b)

Brilliant, I like this approach, it makes core_prio_less() work across
CPUs. So I tested this, together with changing
cpu_prio_less(max, class_pick) to core_prio_less(max, class_pick) in
pick_task(), this problem is gone :-)

I verified with below debug code:

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cb24a0141e57..50658e79363f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3832,6 +3832,14 @@ next_class:;
 
 		WARN_ON_ONCE(!rq_i->core_pick);
 
+		if (rq->core->core_cookie && rq_i->core_pick->core_cookie &&
+			rq->core->core_cookie != rq_i->core_pick->core_cookie) {
+			trace_printk("expect 0x%lx, cpu%d got 0x%lx\n",
+					rq->core->core_cookie, i,
+					rq_i->core_pick->core_cookie);
+			WARN_ON_ONCE(1);
+		}
+
 		rq_i->core_pick->core_occupation = occ;
 
 		if (i == cpu)
-- 
2.19.1.3.ge56e4f7