lkml.org 
[lkml]   [2012]   [Jul]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 01/16] sched: track the runnable average on a per-task entitiy basis
From
Date
On Wed, 2012-06-27 at 19:24 -0700, Paul Turner wrote:
> Instead of tracking averaging the load parented by a cfs_rq, we can track
> entity load directly. With the load for a given cfs_Rq then being the sum of
> its children.
>
> To do this we represent the historical contribution to runnable average within each
> trailing 1024us of execution as the coefficients of a geometric series.
>
> We can express this for a given task t as:
> runnable_sum(t) = \Sum u_i * y^i ,
> load(t) = weight_t * runnable_sum(t) / (\Sum 1024 * y^i)
>
> Where: u_i is the usage in the last i`th 1024us period (approximately 1ms) ~ms
> and y is chosen such that y^k = 1/2. We currently choose k to be 32 which
> roughly translates to about a sched period.
>
> Signed-off-by: Paul Turner <pjt@google.com>
> ---
> include/linux/sched.h | 8 +++
> kernel/sched/debug.c | 4 ++
> kernel/sched/fair.c | 128 +++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 140 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 9dced2e..5bf5c79 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1136,6 +1136,11 @@ struct load_weight {
> unsigned long weight, inv_weight;
> };
>
> +struct sched_avg {
> + u32 runnable_avg_sum, runnable_avg_period;
> + u64 last_runnable_update;
> +};


So we can use u32 because:

n 1
lim n->inf \Sum y^i = --- = ~ 46.66804636511427012122 ; y^32 = 0.5
i=0 1-y

So the values should never be larger than ~47k, right?

/me goes add something like that in a comment.



\
 
 \ /
  Last update: 2012-07-04 18:01    [W:0.244 / U:9.628 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site