On Fri, 2012-10-12 at 10:35 +0100, Jon Medhurst (Tixy) wrote:
> On Fri, 2012-10-12 at 14:46 +0530, Viresh Kumar wrote:
> > Hi Andrey,
> >
> > Please PULL b.L MP V10 branch from my tree.
>
> I've been testing with the v10 branch and with "Enable HMP priority
> filter by default" I have get a crash in select_task_rq_fair() on
> vexpress A9, busy investigating this at the moment...
I've now got to the bottom of the problem...
On homogeneous (non-heterogeneous) systems, arch_get_hmp_domains() still
adds two HMP domains, but the second one is empty. This means that when
CONFIG_SCHED_HMP_PRIO_FILTER is enabled and hmp_down_migration()
unconditionally returns true, then hmp_select_slower_cpu() is called to
select a cpu from this empty domain and returns the value NR_CPUS, which
makes subsequent code blow up.
One question is should hmp_down_migration() return true even when it
hasn't checked there are slower CPUs available?
The attached patch fixes the immediate problem by avoiding the empty
domain (which is probably a good thing anyway), however I wonder if
there are other circumstances in which hmp_select_{slower,fater}_cpu()
can fail? E.g. can tsk_cpus_allowed() ever not intersect with the domain
cpus?
I.e. do we need something like...
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e9dd53c..d3968a6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3217,8 +3217,9 @@ static inline struct hmp_domain *hmp_faster_domain(int
cpu)
static inline unsigned int hmp_select_faster_cpu(struct task_struct *tsk,
int cpu)
{
- return cpumask_any_and(&hmp_faster_domain(cpu)->cpus,
- tsk_cpus_allowed(tsk));
+ unsigned int new_cpu = cpumask_any_and(&hmp_faster_domain(cpu)->cpus,
+ tsk_cpus_allowed(tsk));
+ return new_cpu < NR_CPUS ? new_cpu : cpu;
}
/*
@@ -3228,8 +3229,9 @@ static inline unsigned int hmp_select_faster_cpu(struct
task_struct *tsk,
static inline unsigned int hmp_select_slower_cpu(struct task_struct *tsk,
int cpu)
{
- return cpumask_any_and(&hmp_slower_domain(cpu)->cpus,
- tsk_cpus_allowed(tsk));
+ unsigned int new_cpu = cpumask_any_and(&hmp_slower_domain(cpu)->cpus,
+ tsk_cpus_allowed(tsk));
+ return new_cpu < NR_CPUS ? new_cpu : cpu;
}
static inline void hmp_next_up_delay(struct sched_entity *se, int cpu)
--
Tixy
>From 1cb57d99317f26ffa390544903efb6907e834293 Mon Sep 17 00:00:00 2001
From: Jon Medhurst <t...@linaro.org>
Date: Fri, 12 Oct 2012 13:45:35 +0100
Subject: [PATCH] ARM: sched: Avoid empty 'slow' HMP domain
On homogeneous (non-heterogeneous) systems all CPUs will be declared
'fast' and the slow cpu list will be empty. In this situation we need to
avoid adding an empty slow HMP domain otherwise the scheduler code will
blow up when it attempts to move a task to the slow domain.
Signed-off-by: Jon Medhurst <t...@linaro.org>
---
arch/arm/kernel/topology.c | 10 ++++++----
linaro/configs/vexpress.conf | 2 ++
2 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
index 58dac7a..0b51233 100644
--- a/arch/arm/kernel/topology.c
+++ b/arch/arm/kernel/topology.c
@@ -396,10 +396,12 @@ void __init arch_get_hmp_domains(struct list_head *hmp_domains_list)
* Must be ordered with respect to compute capacity.
* Fastest domain at head of list.
*/
- domain = (struct hmp_domain *)
- kmalloc(sizeof(struct hmp_domain), GFP_KERNEL);
- cpumask_copy(&domain->cpus, &hmp_slow_cpu_mask);
- list_add(&domain->hmp_domains, hmp_domains_list);
+ if(!cpumask_empty(&hmp_slow_cpu_mask)) {
+ domain = (struct hmp_domain *)
+ kmalloc(sizeof(struct hmp_domain), GFP_KERNEL);
+ cpumask_copy(&domain->cpus, &hmp_slow_cpu_mask);
+ list_add(&domain->hmp_domains, hmp_domains_list);
+ }
domain = (struct hmp_domain *)
kmalloc(sizeof(struct hmp_domain), GFP_KERNEL);
cpumask_copy(&domain->cpus, &hmp_fast_cpu_mask);
diff --git a/linaro/configs/vexpress.conf b/linaro/configs/vexpress.conf
index 1ee0101..8b304e1 100644
--- a/linaro/configs/vexpress.conf
+++ b/linaro/configs/vexpress.conf
@@ -58,3 +58,5 @@ CONFIG_NO_HZ=y
CONFIG_SCHED_MC=y
CONFIG_DISABLE_CPU_SCHED_DOMAIN_BALANCE=y
CONFIG_SCHED_HMP=y
+CONFIG_SCHED_HMP_PRIO_FILTER=y
+CONFIG_SCHED_HMP_PRIO_FILTER_VAL=5
--
1.7.10.4
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