linux-kernel - Re: [PATCH] sched: Remove unnecessary initialization in init_cfs

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Message-ID: <20241104121847.GE24862@noisy.programming.kicks-ass.net>
Date: Mon, 4 Nov 2024 13:18:47 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Bitao Hu <yaoma@...ux.alibaba.com>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: Remove unnecessary initialization in
 init_cfs_bandwidth() function

On Mon, Nov 04, 2024 at 08:14:43PM +0800, Bitao Hu wrote:
> The root task group is statically defined, and non-root task groups
> are allocated memory using kmem_cache_alloc() with the __GFP_ZERO
> flag. In both cases, the corresponding 'struct cfs_bandwidth' is a
> block of all-zero memory. Therefore, it is unnecessary to explicitly
> set zeros in the init_cfs_bandwidth() function.
> 
> Signed-off-by: Bitao Hu <yaoma@...ux.alibaba.com>
> ---
>  kernel/sched/fair.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 2d16c8545c71..2fd96641164f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6573,10 +6573,8 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
>  void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, struct cfs_bandwidth *parent)
>  {
>  	raw_spin_lock_init(&cfs_b->lock);
> -	cfs_b->runtime = 0;
>  	cfs_b->quota = RUNTIME_INF;
>  	cfs_b->period = ns_to_ktime(default_cfs_period());
> -	cfs_b->burst = 0;
>  	cfs_b->hierarchical_quota = parent ? parent->hierarchical_quota : RUNTIME_INF;
>  
>  	INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);

But this shows someone thought about it and 0 is the right value, and
not an oversight.