linux-kernel - Re: SCHED_DEADLINE cpudeadline.{h,c} fixup

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Date:	Wed, 18 May 2016 15:22:29 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Tommaso Cucinotta <tommaso.cucinotta@...up.it>
Cc:	luca abeni <luca.abeni@...tn.it>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...il.com>, mingo@...hat.com
Subject: Re: SCHED_DEADLINE cpudeadline.{h,c} fixup

Hi Tommaso,

On 18/05/16 00:43, Tommaso Cucinotta wrote:
> On 17/05/2016 13:46, luca abeni wrote:
> >Maybe the ... change can be split in a separate
> >patch, which is a bugfix (and IMHO uncontroversial)?
> 
> Ok, the bugfix alone might look like the attached. Couldn't avoid
> the little refactoring of the multiple occurrences of the same loop
> up the heap into the heapify_up(), mirroring the heapify() that was
> already there (renamed heapify_down() for clarity).
> 
> I'll rebase the speed-up patch on top of this, if it's a better approach.
> 
> Anyone with further comments?
> 

Couldn't spend any time on this yet, apologies. But, for the next
posting, could you please do it without attaching the patches? I usually
use git send-mail for posting. It would make the review easier, I think.

Best,

- Juri

> Thanks again!
> 
> 	T.
> -- 
> Tommaso Cucinotta, Computer Engineering PhD
> Associate Professor at the Real-Time Systems Laboratory (ReTiS)
> Scuola Superiore Sant'Anna, Pisa, Italy
> http://retis.sssup.it/people/tommaso

> From cfaa75eb77843f7da875a54c7e6631b271bf0663 Mon Sep 17 00:00:00 2001
> From: Tommaso Cucinotta <tommaso.cucinotta@...up.it>
> Date: Tue, 17 May 2016 15:54:11 +0200
> Subject: [PATCH] Deadline wrap-around bugfix for the SCHED_DEADLINE cpu heap.
> 
> ---
>  kernel/sched/cpudeadline.c | 38 +++++++++++++++++++-------------------
>  1 file changed, 19 insertions(+), 19 deletions(-)
> 
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index 5be5882..3c42702 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -41,7 +41,7 @@ static void cpudl_exchange(struct cpudl *cp, int a, int b)
>  	swap(cp->elements[cpu_a].idx, cp->elements[cpu_b].idx);
>  }
>  
> -static void cpudl_heapify(struct cpudl *cp, int idx)
> +static void cpudl_heapify_down(struct cpudl *cp, int idx)
>  {
>  	int l, r, largest;
>  
> @@ -66,20 +66,25 @@ static void cpudl_heapify(struct cpudl *cp, int idx)
>  	}
>  }
>  
> +static void cpudl_heapify_up(struct cpudl *cp, int idx)
> +{
> +	while (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
> +			cp->elements[idx].dl)) {
> +		cpudl_exchange(cp, idx, parent(idx));
> +		idx = parent(idx);
> +	}
> +}
> +
>  static void cpudl_change_key(struct cpudl *cp, int idx, u64 new_dl)
>  {
>  	WARN_ON(idx == IDX_INVALID || !cpu_present(idx));
>  
>  	if (dl_time_before(new_dl, cp->elements[idx].dl)) {
>  		cp->elements[idx].dl = new_dl;
> -		cpudl_heapify(cp, idx);
> +		cpudl_heapify_down(cp, idx);
>  	} else {
>  		cp->elements[idx].dl = new_dl;
> -		while (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
> -					cp->elements[idx].dl)) {
> -			cpudl_exchange(cp, idx, parent(idx));
> -			idx = parent(idx);
> -		}
> +		cpudl_heapify_up(cp, idx);
>  	}
>  }
>  
> @@ -154,24 +159,19 @@ void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid)
>  		cp->size--;
>  		cp->elements[new_cpu].idx = old_idx;
>  		cp->elements[cpu].idx = IDX_INVALID;
> -		while (old_idx > 0 && dl_time_before(
> -				cp->elements[parent(old_idx)].dl,
> -				cp->elements[old_idx].dl)) {
> -			cpudl_exchange(cp, old_idx, parent(old_idx));
> -			old_idx = parent(old_idx);
> -		}
> +		cpudl_heapify_up(cp, old_idx);
>  		cpumask_set_cpu(cpu, cp->free_cpus);
> -                cpudl_heapify(cp, old_idx);
> +                cpudl_heapify_down(cp, old_idx);
>  
>  		goto out;
>  	}
>  
>  	if (old_idx == IDX_INVALID) {
> -		cp->size++;
> -		cp->elements[cp->size - 1].dl = 0;
> -		cp->elements[cp->size - 1].cpu = cpu;
> -		cp->elements[cpu].idx = cp->size - 1;
> -		cpudl_change_key(cp, cp->size - 1, dl);
> +		int size1 = cp->size++;
> +		cp->elements[size1].dl = dl;
> +		cp->elements[size1].cpu = cpu;
> +		cp->elements[cpu].idx = size1;
> +		cpudl_heapify_up(cp, size1);
>  		cpumask_clear_cpu(cpu, cp->free_cpus);
>  	} else {
>  		cpudl_change_key(cp, old_idx, dl);
> -- 
> 2.7.4
>