Re: [PATCH 2/3] sched: Add aggressive load balancing for certain situations

[Peter Zijlstra <peterz@infradead.org>]

On Sat, 2009-10-24 at 13:04 -0700, Arjan van de Ven wrote:
> Subject: sched: Add aggressive load balancing for certain situations
> From: Arjan van de Ven <arjan@linux.intel.com>
> 
> The scheduler, in it's "find idlest group" function currently has an unconditional
> threshold for an imbalance, before it will consider moving a task.
> 
> However, there are situations where this is undesireable, and we want to opt in to a
> more aggressive load balancing algorithm to minimize latencies.
> 
> This patch adds the infrastructure for this and also adds two cases for which
> we select the aggressive approach
> 1) From interrupt context. Events that happen in irq context are very likely,
>    as a heuristic, to show latency sensitive behavior
> 2) When doing a wake_up() and the scheduler domain we're investigating has the
>    flag set that opts in to load balancing during wake_up()
>    (for example the SMT/HT domain)
> 
> 
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>



> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index 4e777b4..fe9b95b 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -1246,7 +1246,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
>   */
>  static struct sched_group *
>  find_idlest_group(struct sched_domain *sd, struct task_struct *p,
> -		  int this_cpu, int load_idx)
> +		  int this_cpu, int load_idx, int agressive)
>  {

can't we fold that into load_idx? like -1 or something?