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  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]
Date:	Tue, 29 Jul 2014 16:49:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, vincent.guittot@...aro.org,
	mikey@...ling.org, mingo@...nel.org, jhladky@...hat.com,
	ktkhai@...allels.com, tim.c.chen@...ux.intel.com,
	nicolas.pitre@...aro.org
Subject: Re: [PATCH 1/2] sched: fix and clean up calculate_imbalance

On Mon, Jul 28, 2014 at 02:16:27PM -0400, riel@...hat.com wrote:
> @@ -6221,16 +6221,16 @@ void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
>   */
>  static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
>  {
> -	unsigned long max_pull, load_above_capacity = ~0UL;
>  	struct sg_lb_stats *local, *busiest;
>  
>  	local = &sds->local_stat;
>  	busiest = &sds->busiest_stat;
>  
> -	if (busiest->group_imb) {
> +	if (busiest->avg_load <= sds->avg_load) {
>  		/*
> -		 * In the group_imb case we cannot rely on group-wide averages
> -		 * to ensure cpu-load equilibrium, look at wider averages. XXX
> +		 * Busiest got picked because it is overloaded or imbalanced,
> +		 * but does not have an above-average load. Look at wider
> +		 * averages.
>  		 */
>  		busiest->load_per_task =
>  			min(busiest->load_per_task, sds->avg_load);

I don't think that's right, this code is really for imbalance only,
although I'm now wondering why (again)..

So currently the only other case is overloaded (since, as you noticed,
we don't balance for !overloaded) and that explicitly doesn't use it. So
making the overloaded case use this doesn't make sense.

> @@ -6247,32 +6247,15 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
>  		return fix_small_imbalance(env, sds);
>  	}
>  
> -	if (!busiest->group_imb) {
> -		/*
> -		 * Don't want to pull so many tasks that a group would go idle.
> -		 * Except of course for the group_imb case, since then we might
> -		 * have to drop below capacity to reach cpu-load equilibrium.
> -		 */
> -		load_above_capacity =
> -			(busiest->sum_nr_running - busiest->group_capacity_factor);
> -
> -		load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_CAPACITY_SCALE);
> -		load_above_capacity /= busiest->group_capacity;
> -	}

I think we want to retain that, esp. for the overloaded case. So that
wants to be:

	if (busiest->sum_nr_running > busiest->group_capacity_factor)

Clearly it doesn't make sense for the !overload case, and we explicitly
want to avoid it in the imb case.
--
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/

Powered by blists - more mailing lists