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Message-ID: <52679BD6.6090507@linux.vnet.ibm.com>
Date: Wed, 23 Oct 2013 15:20:14 +0530
From: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Mike Galbraith <bitbucket@...ine.de>,
Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...nel.org>,
Michael Neuling <mikey@...ling.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
linux-kernel@...r.kernel.org, Anton Blanchard <anton@...ba.org>,
linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/3] sched: Fix nohz_kick_needed to consider the nr_busy
of the parent domain's group
Hi Peter
On 10/23/2013 03:41 AM, Peter Zijlstra wrote:
> This nohz stuff really needs to be re-thought and made more scalable --
> its a royal pain :/
Why not do something like the below instead? It does the following.
This patch introduces sd_busy just like your suggested patch, except that
it points to the parent of the highest level sched domain which has the
SD_SHARE_PKG_RESOURCES set and initializes it in update_top_cache_domain().
This is the sched domain that is relevant in nohz_kick_needed().
sd_set_sd_state_busy(), sd_set_sd_state_idle() and nohz_kick_needed() query
and update *only* this sched domain(sd_busy) for nr_busy_cpus. They are the
only users of this parameter. While we are at it, we might as well change
the nohz_idle parameter to be updated at the sd_busy domain level alone and
not the base domain level of a CPU. This will unify the concept of busy cpus
at just one level of sched domain.
There is no need to iterate through all levels of sched domains of a cpu to
update nr_busy_cpus since it is irrelevant at all other sched domains except
at sd_busy level.
De-couple asymmetric load balancing from the nr_busy parameter which the
PATCH 2/3 anyway does. sd_busy therefore is irrelevant for asymmetric load
balancing.
Regards
Preeti U Murthy
--------------------START_PATCH-------------------------------
sched: Fix nohz_kick_needed()
---
kernel/sched/core.c | 4 ++++
kernel/sched/fair.c | 40 ++++++++++++++++++++++------------------
kernel/sched/sched.h | 1 +
3 files changed, 27 insertions(+), 18 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c06b8d3..c1dd11c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5271,6 +5271,7 @@ DEFINE_PER_CPU(struct sched_domain *, sd_llc);
DEFINE_PER_CPU(int, sd_llc_size);
DEFINE_PER_CPU(int, sd_llc_id);
DEFINE_PER_CPU(struct sched_domain *, sd_numa);
+DEFINE_PER_CPU(struct sched_domain *, sd_busy);
static void update_top_cache_domain(int cpu)
{
@@ -5290,6 +5291,9 @@ static void update_top_cache_domain(int cpu)
sd = lowest_flag_domain(cpu, SD_NUMA);
rcu_assign_pointer(per_cpu(sd_numa, cpu), sd);
+
+ sd = highest_flag_domain(cpu, SD_SHARE_PKG_RESOURCES)->parent;
+ rcu_assign_pointer(per_cpu(sd_busy, cpu), sd);
}
/*
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 813dd61..71e6f14 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6515,16 +6515,16 @@ static inline void nohz_balance_exit_idle(int cpu)
static inline void set_cpu_sd_state_busy(void)
{
struct sched_domain *sd;
+ int cpu = smp_processor_id();
rcu_read_lock();
- sd = rcu_dereference_check_sched_domain(this_rq()->sd);
+ sd = per_cpu(sd_busy, cpu);
if (!sd || !sd->nohz_idle)
goto unlock;
sd->nohz_idle = 0;
- for (; sd; sd = sd->parent)
- atomic_inc(&sd->groups->sgp->nr_busy_cpus);
+ atomic_inc(&sd->groups->sgp->nr_busy_cpus);
unlock:
rcu_read_unlock();
}
@@ -6532,16 +6532,16 @@ unlock:
void set_cpu_sd_state_idle(void)
{
struct sched_domain *sd;
+ int cpu = smp_processor_id();
rcu_read_lock();
- sd = rcu_dereference_check_sched_domain(this_rq()->sd);
+ sd = per_cpu(sd_busy, cpu);
if (!sd || sd->nohz_idle)
goto unlock;
sd->nohz_idle = 1;
- for (; sd; sd = sd->parent)
- atomic_dec(&sd->groups->sgp->nr_busy_cpus);
+ atomic_dec(&sd->groups->sgp->nr_busy_cpus);
unlock:
rcu_read_unlock();
}
@@ -6748,6 +6748,9 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
{
unsigned long now = jiffies;
struct sched_domain *sd;
+ struct sched_group *sg;
+ struct sched_group_power *sgp;
+ int nr_busy;
if (unlikely(idle_cpu(cpu)))
return 0;
@@ -6773,22 +6776,23 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
goto need_kick;
rcu_read_lock();
- for_each_domain(cpu, sd) {
- struct sched_group *sg = sd->groups;
- struct sched_group_power *sgp = sg->sgp;
- int nr_busy = atomic_read(&sgp->nr_busy_cpus);
+ sd = per_cpu(sd_busy, cpu);
- if (sd->flags & SD_SHARE_PKG_RESOURCES && nr_busy > 1)
- goto need_kick_unlock;
+ if (sd) {
+ sg = sd->groups;
+ sgp = sg->sgp;
+ nr_busy = atomic_read(&sgp->nr_busy_cpus);
- if (sd->flags & SD_ASYM_PACKING && nr_busy != sg->group_weight
- && (cpumask_first_and(nohz.idle_cpus_mask,
- sched_domain_span(sd)) < cpu))
+ if (nr_busy > 1)
goto need_kick_unlock;
-
- if (!(sd->flags & (SD_SHARE_PKG_RESOURCES | SD_ASYM_PACKING)))
- break;
}
+
+ sd = highest_flag_domain(cpu, SD_ASYM_PACKING);
+
+ if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
+ sched_domain_span(sd)) < cpu))
+ goto need_kick_unlock;
+
rcu_read_unlock();
return 0;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ffc7087..0f1253f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -623,6 +623,7 @@ DECLARE_PER_CPU(struct sched_domain *, sd_llc);
DECLARE_PER_CPU(int, sd_llc_size);
DECLARE_PER_CPU(int, sd_llc_id);
DECLARE_PER_CPU(struct sched_domain *, sd_numa);
+DECLARE_PER_CPU(struct sched_domain *, sd_busy);
struct sched_group_power {
atomic_t ref;
--
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