Re: [RFC][Patch 02/18] sched: increase SCHED_LOAD_SCALE resolution

["Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>]

On Wed, 20 Apr 2011 13:51:21 -0700, Nikhil Rao <ncrao@google.com> wrote:
> Introduce SCHED_LOAD_RESOLUTION, which scales is added to SCHED_LOAD_SHIFT and
> increases the resolution of SCHED_LOAD_SCALE. This patch sets the value of
> SCHED_LOAD_RESOLUTION to 10, scaling up the weights for all sched entities by
> a factor of 1024. With this extra resolution, we can handle deeper cgroup
> hiearchies and the scheduler can do better shares distribution and load
> load balancing on larger systems (especially for low weight task groups).
> 
> This does not change the existing user interface, the scaled weights are only
> used internally. We do not modify prio_to_weight values or inverses, but use
> the original weights when calculating the inverse which is used to scale
> execution time delta in calc_delta_mine(). This ensures we do not lose accuracy
> when accounting time to the sched entities.
> 
> Signed-off-by: Nikhil Rao <ncrao@google.com>
> ---
>  include/linux/sched.h |    3 ++-
>  kernel/sched.c        |   18 ++++++++++--------
>  2 files changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 8d1ff2b..d2c3bab 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -794,7 +794,8 @@ enum cpu_idle_type {
>  /*
>   * Increase resolution of nice-level calculations:
>   */
> -#define SCHED_LOAD_SHIFT	10
> +#define SCHED_LOAD_RESOLUTION	10
> +#define SCHED_LOAD_SHIFT	(10 + SCHED_LOAD_RESOLUTION)
>  #define SCHED_LOAD_SCALE	(1L << SCHED_LOAD_SHIFT)
> 
>  /*
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 50f97cc..bfee8ff 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -293,7 +293,7 @@ static DEFINE_SPINLOCK(task_group_lock);
>   *  limitation from this.)
>   */
>  #define MIN_SHARES	2
> -#define MAX_SHARES	(1UL << 18)
> +#define MAX_SHARES	(1UL << 28)
Shouldn't this change depend on SCHED_LOAD_RESOLUTION?

#define MAX_SHARES	(1UL << (18 + SCHED_LOAD_RESOLUTION))

Nikunj