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Date: Sun, 24 Mar 2024 01:16:20 +0000
From: Qais Yousef <qyousef@layalina.io>
To: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org,
	dietmar.eggemann@arm.com, linux-kernel@vger.kernel.org,
	vschneid@redhat.com, qperret@google.com
Subject: Re: [PATCH v2 2/2] sched/fair: Use helper functions to access
 rd->overload
Message-ID: <20240324011620.f3mmywh44htvlb5m@airbuntu>
References: <20240322141632.28654-1-sshegde@linux.ibm.com>
 <20240322141632.28654-3-sshegde@linux.ibm.com>
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In-Reply-To: <20240322141632.28654-3-sshegde@linux.ibm.com>

On 03/22/24 19:46, Shrikanth Hegde wrote:
> rd->overload is accessed at multiple places. Instead it could use helper
> get/set functions. This would make the code more readable and easy to
> maintain.
> 
> No change in functionality intended.
> 
> Suggested-by: Qais Yousef <qyousef@layalina.io>

Thanks for following up!

> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>  kernel/sched/fair.c  |  7 ++++---
>  kernel/sched/sched.h | 14 ++++++++++++--
>  2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index eeebadd7d9ae..cee99c93e6a4 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10621,8 +10621,9 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
> 
>  	if (!env->sd->parent) {
>  		/* update overload indicator if we are at root domain */
> -		if (READ_ONCE(env->dst_rq->rd->overload) != (sg_status & SG_OVERLOAD))
> -			WRITE_ONCE(env->dst_rq->rd->overload, sg_status & SG_OVERLOAD);
> +		if (is_rd_overloaded(env->dst_rq->rd) != (sg_status & SG_OVERLOAD))
> +			set_rd_overload_status(env->dst_rq->rd,
> +					       sg_status & SG_OVERLOAD);

A bit picky, but..

Wouldn't it be better to encapsulate the check of whether we're writing a new
value inside set_rd_overload_status()? Only write if it the value changed and
all future users wouldn't care then.

I think no need to wrap the line too.

> 
>  		/* Update over-utilization (tipping point, U >= 0) indicator */
>  		set_rd_overutilized_status(env->dst_rq->rd,
> @@ -12344,7 +12345,7 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
>  	rcu_read_lock();
>  	sd = rcu_dereference_check_sched_domain(this_rq->sd);
> 
> -	if (!READ_ONCE(this_rq->rd->overload) ||
> +	if (!is_rd_overloaded(this_rq->rd) ||
>  	    (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
> 
>  		if (sd)
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 41024c1c49b4..c91eb8811bef 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -918,6 +918,16 @@ extern void rq_attach_root(struct rq *rq, struct root_domain *rd);
>  extern void sched_get_rd(struct root_domain *rd);
>  extern void sched_put_rd(struct root_domain *rd);
> 
> +static inline int is_rd_overloaded(struct root_domain *rd)
> +{
> +	return READ_ONCE(rd->overload);
> +}
> +
> +static inline void set_rd_overload_status(struct root_domain *rd, int status)
> +{
> +	WRITE_ONCE(rd->overload, status);
> +}
> +
>  #ifdef HAVE_RT_PUSH_IPI
>  extern void rto_push_irq_work_func(struct irq_work *work);
>  #endif
> @@ -2518,8 +2528,8 @@ static inline void add_nr_running(struct rq *rq, unsigned count)
> 
>  #ifdef CONFIG_SMP
>  	if (prev_nr < 2 && rq->nr_running >= 2) {
> -		if (!READ_ONCE(rq->rd->overload))
> -			WRITE_ONCE(rq->rd->overload, 1);
> +		if (!is_rd_overloaded(rq->rd))
> +			set_rd_overload_status(rq->rd, 1);

While at it, could you write SG_OVERLOAD instead of 1?

Both patches LGTM otherwise

Reviewed-by: Qais Yousef <qyousef@layalina.io>


Thanks!

--
Qais Yousef

>  	}
>  #endif
> 
> --
> 2.39.3
>