linux-kernel - Re: [RFC 3/4] sched/idle: Disable idle call on least latency requirements

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Date:   Fri, 8 May 2020 14:06:01 +0530
From:   Pavan Kondeti <pkondeti@...eaurora.org>
To:     Parth Shah <parth@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, qais.yousef@....com,
        chris.hyser@...cle.com, valentin.schneider@....com,
        rjw@...ysocki.net
Subject: Re: [RFC 3/4] sched/idle: Disable idle call on least latency
 requirements

On Thu, May 07, 2020 at 07:07:22PM +0530, Parth Shah wrote:
> Restrict the call to deeper idle states when the given CPU has been set for
> the least latency requirements
> 
> Signed-off-by: Parth Shah <parth@...ux.ibm.com>
> ---
>  kernel/sched/idle.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index b743bf38f08f..85d72a6e2521 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -262,7 +262,8 @@ static void do_idle(void)
>  		 * broadcast device expired for us, we don't want to go deep
>  		 * idle as we know that the IPI is going to arrive right away.
>  		 */
> -		if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
> +		if (cpu_idle_force_poll || tick_check_broadcast_expired() ||
> +		    per_cpu(nr_lat_sensitive, cpu)) {
>  			tick_nohz_idle_restart_tick();
>  			cpu_idle_poll();
>  		} else {
> -- 
> 2.17.2
> 

Since nr_lat_sensitive updates can happen remotely (when a latency sensitive
task becomes non-latency sensitive task), we may need to add this condition
in cpu_idle_poll() as well.

Thanks,
Pavan
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.