linux-kernel - Re: [RFC PATCHC 3/3] sched/fair: use the idle state info to choose the idlest cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140415130301.GL11182@twins.programming.kicks-ass.net>
Date:	Tue, 15 Apr 2014 15:03:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, rjw@...ysocki.net,
	nicolas.pitre@...aro.org, linux-pm@...r.kernel.org,
	alex.shi@...aro.org, vincent.guittot@...aro.org,
	morten.rasmussen@....com
Subject: Re: [RFC PATCHC 3/3] sched/fair: use the idle state info to choose
 the idlest cpu

On Fri, Mar 28, 2014 at 01:29:56PM +0100, Daniel Lezcano wrote:
> @@ -4336,20 +4337,53 @@ static int
>  find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
>  {
>  	unsigned long load, min_load = ULONG_MAX;
> -	int idlest = -1;
> +	unsigned int min_exit_latency = UINT_MAX;
> +	u64 idle_stamp, min_idle_stamp = ULONG_MAX;
> +
> +	struct rq *rq;
> +	struct cpuidle_power *power;
> +
> +	int cpu_idle = -1;
> +	int cpu_busy = -1;
>  	int i;
>  
>  	/* Traverse only the allowed CPUs */
>  	for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) {
> -		load = weighted_cpuload(i);
>  
> -		if (load < min_load || (load == min_load && i == this_cpu)) {
> -			min_load = load;
> -			idlest = i;
> +		if (idle_cpu(i)) {
> +
> +			rq = cpu_rq(i);
> +			power = rq->power;
> +			idle_stamp = rq->idle_stamp;
> +
> +			/* The cpu is idle since a shorter time */
> +			if (idle_stamp < min_idle_stamp) {
> +				min_idle_stamp = idle_stamp;
> +				cpu_idle = i;
> +				continue;
> +			}
> +
> +			/* The cpu is idle but the exit_latency is shorter */
> +			if (power && power->exit_latency < min_exit_latency) {
> +				min_exit_latency = power->exit_latency;
> +				cpu_idle = i;
> +				continue;
> +			}

Aside from the arguments made by Nico (which I agree with), depending on
the life time rules of the power object we might need
smp_read_barrier_depends() between reading and using.

If all these objects are static and never change content we do not, if
there's dynamic objects involved we probably should.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/