lkml.org 
[lkml]   [2014]   [Mar]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC 3/4] sched: fix computed capacity for HMP
Date
The current sg_capacity solves the ghost cores issue for SMT system and
cluster made of big cores which have a cpu_power above SCHED_POWER_SCALE at
core level. But it still removes some real cores of a cluster made of LITTLE
cores which have a cpu_power below SCHED_POWER_SCALE.

Instead of using the power_orig to detect SMT system and compute a smt factor
that will be used to calculate the real number of cores, we set a core_fct
field when building the sched_domain topology. We can detect SMT system thanks
to SD_SHARE_CPUPOWER flag and set core_fct to know how many CPUs per core we
have. The core_fct will ensure that sg_capacity will return cores capacity of
a SMT system and will not remove any real core of LITTLE cluster.

This method also fixes a use case where the capacity of a SMT system was
overrated.
Let take the example of a system made of 8 cores HT system:
At CPU level, sg_capacity is cap to a maximum capacity of 8 whereas
DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE) returns 9.
((589*16) / 1024) = 9.3
Now if 2 CPUs (1 core) are fully loaded by rt tasks, sg_capacity still returns
a capacity of 8 whereas it should return a capacity of 7. This happen because
DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE) is still above 7.5:
((589*14) / 1024) = 8.05

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/core.c | 7 +++++++
kernel/sched/fair.c | 6 ++----
kernel/sched/sched.h | 2 +-
3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f9d9776..5b20b27 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5844,6 +5844,13 @@ static void init_sched_groups_power(int cpu, struct sched_domain *sd)

WARN_ON(!sg);

+ if (!sd->child)
+ sg->core_fct = 1;
+ else if (sd->child->flags & SD_SHARE_CPUPOWER)
+ sg->core_fct = cpumask_weight(sched_group_cpus(sg));
+ else
+ sg->core_fct = sd->child->groups->core_fct;
+
do {
sg->group_weight = cpumask_weight(sched_group_cpus(sg));
sg = sg->next;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ed42061..7387c05 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5773,12 +5773,10 @@ static inline int sg_capacity(struct lb_env *env, struct sched_group *group)
power = group->sgp->power;
power_orig = group->sgp->power_orig;
cpus = group->group_weight;
+ smt = group->core_fct;

- /* smt := ceil(cpus / power), assumes: 1 < smt_power < 2 */
- smt = DIV_ROUND_UP(SCHED_POWER_SCALE * cpus, power_orig);
- capacity = cpus / smt; /* cores */
+ capacity = DIV_ROUND_CLOSEST(power * cpus, power_orig * smt);

- capacity = min_t(unsigned, capacity, DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE));
if (!capacity)
capacity = fix_small_capacity(env->sd, group);

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c9007f2..46c3784 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -759,7 +759,7 @@ struct sched_group {
struct sched_group *next; /* Must be a circular list */
atomic_t ref;

- unsigned int group_weight;
+ unsigned int group_weight, core_fct;
struct sched_group_power *sgp;

/*
--
1.9.0


\
 
 \ /
  Last update: 2014-03-28 15:01    [W:0.109 / U:4.972 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site