linux-kernel - Re: [PATCH v2] sched_ext: Replace hardcoding with macro and minor typo fix

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Message-ID: <ZzYvf2L3rlmjuKzh@slm.duckdns.org>
Date: Thu, 14 Nov 2024 07:12:31 -1000
From: Tejun Heo <tj@...nel.org>
To: Zhao Mengmeng <zhaomzhao@....com>
Cc: void@...ifault.com, zhaomengmeng@...inos.cn,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched_ext: Replace hardcoding with macro and minor
 typo fix

Hello,

On Wed, Nov 13, 2024 at 10:59:08AM +0800, Zhao Mengmeng wrote:
> From: Zhao Mengmeng <zhaomengmeng@...inos.cn>
> 
> 1. replace hardcoding with SCX_KF_UNLOCKED.
> 2. scx_next_task_picked() has been replaced with siwtch_class().
> 3. minor typo fixes.
> 
> Signed-off-by: Zhao Mengmeng <zhaomengmeng@...inos.cn>
> ---
>  kernel/sched/ext.c             | 6 +++---
>  tools/sched_ext/scx_qmap.bpf.c | 2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 1b1c33f12dd7..832f77d1d318 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -2759,10 +2759,10 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
>  		 * If the previous sched_class for the current CPU was not SCX,
>  		 * notify the BPF scheduler that it again has control of the
>  		 * core. This callback complements ->cpu_release(), which is
> -		 * emitted in scx_next_task_picked().
> +		 * emitted in switch_class().
>  		 */
>  		if (SCX_HAS_OP(cpu_acquire))
> -			SCX_CALL_OP(0, cpu_acquire, cpu_of(rq), NULL);
> +			SCX_CALL_OP(SCX_KF_UNLOCKED, cpu_acquire, cpu_of(rq), NULL);

I think this is actually a bug. David, shouldn't this be SCX_KF_REST?

>  		rq->scx.cpu_released = false;
>  	}
>  
> @@ -6096,7 +6096,7 @@ static void kick_cpus_irq_workfn(struct irq_work *irq_work)
>  		if (cpu != cpu_of(this_rq)) {
>  			/*
>  			 * Pairs with smp_store_release() issued by this CPU in
> -			 * scx_next_task_picked() on the resched path.
> +			 * switch_class() on the resched path.
>  			 *
>  			 * We busy-wait here to guarantee that no other task can
>  			 * be scheduled on our core before the target CPU has
> diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
> index ee264947e0c3..f230641929ec 100644
> --- a/tools/sched_ext/scx_qmap.bpf.c
> +++ b/tools/sched_ext/scx_qmap.bpf.c
> @@ -5,7 +5,7 @@
>   * There are five FIFOs implemented using BPF_MAP_TYPE_QUEUE. A task gets
>   * assigned to one depending on its compound weight. Each CPU round robins
>   * through the FIFOs and dispatches more from FIFOs with higher indices - 1 from
> - * queue0, 2 from queue1, 4 from queue2 and so on.
> + * queue0, 2 from queue1, 3 from queue2 and so on.

The number to dispatch is determined by:

  cpuc->dsp_cnt = 1 << cpuc->dsp_idx;

I think the existing comment is correct.

Thasnks.

-- 
tejun