linux-kernel - Re: [RFC PATCH 2/4] SCHED_DEADLINE cpu heap code clarification/refactory.

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Date:	Mon, 1 Aug 2016 17:30:22 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Tommaso Cucinotta <tommaso.cucinotta@...up.it>
Cc:	Luca Abeni <luca.abeni@...tn.it>,
	Juri Lelli <juri.lelli@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/4] SCHED_DEADLINE cpu heap code
 clarification/refactory.

Hi,

nice clean-up. Maybe change the subject to something like
"sched/deadline: refactor cpu heap code" ?

On 19/07/16 11:44, Tommaso Cucinotta wrote:

This change does two things:

> 1. heapify up factored out in new dedicated function heapify_up()
>    (avoids repeatition of same code)

s/repeatition/repetition/

> 2. call to cpudl_change_key() replaced with heapify_up() when
>    cpudl_set actually inserts a new node in the heap
> 

Maybe we want a separate patch (we usually want 1 patch - 1 change) ?

> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Juri Lelli <juri.lelli@....com>
> Cc: Luca Abeni <luca.abeni@...tn.it>
> Reviewed-by: Luca Abeni <luca.abeni@...tn.it>
> Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@...up.it>
> ---
>  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 d418449..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);

I think this line was already whitespace damaged. Could you fix it (with
a proper tab) in next version?

>  
>  		goto out;
>  	}
>  
>  	if (old_idx == IDX_INVALID) {
> -		cp->size++;
> -		cp->elements[cp->size - 1].dl = dl;
> -		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++;

s/size1/new_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);

We also seem to do almost the same ("cp->size - 1" mutliple times and
then cp->size--) up above, !is_valid branch. Maybe we want to clean
that up as well?

Thanks,

- Juri