Re: [patch 1/2] sched: move periodic share updates to entity_tick()

[Mike Galbraith <efault@gmx.de>]

On Thu, 2010-12-16 at 12:03 +0100, Peter Zijlstra wrote:
> I made that:

Box is ill, I'll test these as soon as it's all better.

> ---
> Subject: sched: Move periodic share updates to entity_tick()
> From: Paul Turner <pjt@google.com>
> Date: Wed, 15 Dec 2010 19:10:17 -0800
> 
> Long running entities that do not block (dequeue) require periodic updates to
> maintain accurate share values.  (Note: group entities with several threads are
> quite likely to be non-blocking in many circumstances).
> 
> By virtue of being long-running however, we will see entity ticks (otherwise
> the required update occurs in dequeue/put and we are done).  Thus we can move
> the detection (and associated work) for these updates into the periodic path.
> 
> This restores the 'atomicity' of update_curr() with respect to accounting.
> 
> Signed-off-by: Paul Turner <pjt@google.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> LKML-Reference: <20101216031038.067028969@google.com>
> ---
>  kernel/sched_fair.c |   21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> Index: linux-2.6/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_fair.c
> +++ linux-2.6/kernel/sched_fair.c
> @@ -564,10 +564,6 @@ __update_curr(struct cfs_rq *cfs_rq, str
>  
>  #if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED
>  	cfs_rq->load_unacc_exec_time += delta_exec;
> -	if (cfs_rq->load_unacc_exec_time > sysctl_sched_shares_window) {
> -		update_cfs_load(cfs_rq, 0);
> -		update_cfs_shares(cfs_rq, 0);
> -	}
>  #endif
>  }
>  
> @@ -809,6 +805,14 @@ static void update_cfs_shares(struct cfs
>  
>  	reweight_entity(cfs_rq_of(se), se, shares);
>  }
> +
> +static void update_entity_shares_tick(struct cfs_rq *cfs_rq)
> +{
> +	if (cfs_rq->load_unacc_exec_time > sysctl_sched_shares_window) {
> +		update_cfs_load(cfs_rq, 0);
> +		update_cfs_shares(cfs_rq, 0);
> +	}
> +}
>  #else /* CONFIG_FAIR_GROUP_SCHED */
>  static void update_cfs_load(struct cfs_rq *cfs_rq, int global_update)
>  {
> @@ -817,6 +821,10 @@ static void update_cfs_load(struct cfs_r
>  static inline void update_cfs_shares(struct cfs_rq *cfs_rq, long weight_delta)
>  {
>  }
> +
> +static inline void update_entity_shares_tick(struct cfs_rq *cfs_rq)
> +{
> +}
>  #endif /* CONFIG_FAIR_GROUP_SCHED */
>  
>  static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
> @@ -1133,6 +1141,11 @@ entity_tick(struct cfs_rq *cfs_rq, struc
>  	 */
>  	update_curr(cfs_rq);
>  
> +	/*
> +	 * Update share accounting for long-running entities.
> +	 */
> +	update_entity_shares_tick(cfs_rq);
> +
>  #ifdef CONFIG_SCHED_HRTICK
>  	/*
>  	 * queued ticks are scheduled to match the slice, so don't bother
>