On 30 August 2014 19:07, Preeti U Murthy [off-list ref] wrote:

Hi Vincent,

On 08/26/2014 04:36 PM, Vincent Guittot wrote:

quoted

capacity_orig is only changed for system with a SMT sched_domain level in order

I think I had asked this before, but why only capacity_orig? The
capacity of a group is also being updated the same way. This patch fixes
the capacity of a group to reflect the capacity of the heterogeneous
CPUs in it, this capacity being both the full capacity of the group:
capacity_orig and the capacity available for the fair tasks. So I feel
in the subject as well as the changelog it would suffice to say 'capacity'.

IIRC, we discussed that point on a former version. The patch changes
only the behavior of capacity_orig but the behavior of capacity stays
unchanged as all archs can already set the capacity whereas the
capacity_orig was configurable only if the SD_SHARE_CPUCAPACITY was
set in the sched_domain. This is no more the case with this patch
which creates arch_scale_cpu_capacity for setting capacity_orig.

quoted

to reflect the lower capacity of CPUs. Heterogenous system also have to reflect an
original capacity that is different from the default value.

Create a more generic function arch_scale_cpu_capacity that can be also used by
non SMT platform to set capacity_orig.

The weak behavior of arch_scale_cpu_capacity is the previous SMT one in order to
keep backward compatibility in the use of capacity_orig.

arch_scale_smt_capacity and default_scale_smt_capacity have been removed as
they were not use elsewhere than in arch_scale_cpu_capacity.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/fair.c | 25 ++++++-------------------
 1 file changed, 6 insertions(+), 19 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b85e9f7..8176bda 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c

@@ -5705,19 +5705,12 @@ unsigned long __weak arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
      return default_scale_capacity(sd, cpu);
 }

-static unsigned long default_scale_smt_capacity(struct sched_domain *sd, int cpu)
+unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
 {
-     unsigned long weight = sd->span_weight;
-     unsigned long smt_gain = sd->smt_gain;
+     if ((sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1))
+             return sd->smt_gain / sd->span_weight;

-     smt_gain /= weight;
-
-     return smt_gain;
-}
-
-unsigned long __weak arch_scale_smt_capacity(struct sched_domain *sd, int cpu)
-{
-     return default_scale_smt_capacity(sd, cpu);
+     return SCHED_CAPACITY_SCALE;
 }

 static unsigned long scale_rt_capacity(int cpu)

@@ -5756,18 +5749,12 @@ static unsigned long scale_rt_capacity(int cpu)

 static void update_cpu_capacity(struct sched_domain *sd, int cpu)
 {
-     unsigned long weight = sd->span_weight;
      unsigned long capacity = SCHED_CAPACITY_SCALE;
      struct sched_group *sdg = sd->groups;

-     if ((sd->flags & SD_SHARE_CPUCAPACITY) && weight > 1) {
-             if (sched_feat(ARCH_CAPACITY))

Aren't you missing this check above? I understand that it is not
crucial, but that would also mean removing ARCH_CAPACITY sched_feat
altogether, wouldn't it?

Peter has proposed to remove all those checks and to keep only the
default behavior because no arch uses arch_scale_smt_capacity.
Then, ARCH_CAPACITY is still used in update_cpu_capacity

Regards,
Vincent

Regards
Preeti U Murthy

quoted

-                     capacity *= arch_scale_smt_capacity(sd, cpu);
-             else
-                     capacity *= default_scale_smt_capacity(sd, cpu);
+     capacity *= arch_scale_cpu_capacity(sd, cpu);

-             capacity >>= SCHED_CAPACITY_SHIFT;
-     }
+     capacity >>= SCHED_CAPACITY_SHIFT;

      sdg->sgc->capacity_orig = capacity;