linux-kernel - Re: [PATCH 1/2] sched_ext: Track currently locked rq

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Message-ID: <aAaWbDu-WKEhQYq_@slm.duckdns.org>
Date: Mon, 21 Apr 2025 09:03:08 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched_ext: Track currently locked rq

Hello,

On Sun, Apr 20, 2025 at 09:30:21PM +0200, Andrea Righi wrote:
...
> +static inline struct rq *scx_locked_rq(void)
> +{
> +	return __this_cpu_read(locked_rq);
> +}
> +
> +#define SCX_CALL_OP(mask, rq, op, args...)					\
>  do {										\
> +	update_locked_rq(rq);							\

Minor but why not

        if (rq)
                update_locked_rq(rq);

here too to be symmetric?

>  	if (mask) {								\
>  		scx_kf_allow(mask);						\
>  		scx_ops.op(args);						\
> @@ -1125,11 +1155,15 @@ do {										\
>  	} else {								\
>  		scx_ops.op(args);						\
>  	}									\
> +	if (rq)									\
> +		update_locked_rq(NULL);						\

Or alternatively, drop `if (rq)` from both places. That's simpler and given
that all the hot paths are called with rq locked, that may be *minutely*
faster.

> @@ -2174,7 +2210,7 @@ static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
>  	WARN_ON_ONCE(*ddsp_taskp);
>  	*ddsp_taskp = p;
>  
> -	SCX_CALL_OP_TASK(SCX_KF_ENQUEUE, enqueue, p, enq_flags);
> +	SCX_CALL_OP_TASK(SCX_KF_ENQUEUE, rq, enqueue, p, enq_flags);

Let's do SCX_CALL_OP_TASK(SCX_FK_ENQUEUE, enqueue, rq, p, enq_flags) so that
the static parts of the invocation are grouped together and we usually have
@rq and @p next to each other when they're used as parameters.

Thanks.

-- 
tejun