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Subject[PATCH 3/3] workqueue: Schedule work on non-idle cpu instead of current one
Date
Workqueues queues work on current cpu, if the caller haven't passed a preferred
cpu. This may wake up an idle CPU, which is actually not required.

This work can be processed by any CPU and so we must select a non-idle CPU here.
This patch adds in support in workqueue framework to get preferred CPU details
from the scheduler, instead of using current CPU.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
arch/arm/Kconfig | 11 +++++++++++
kernel/workqueue.c | 25 ++++++++++++++++++-------
2 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5944511..da17bd0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1594,6 +1594,17 @@ config HMP_SLOW_CPU_MASK
Specify the cpuids of the slow CPUs in the system as a list string,
e.g. cpuid 0+1 should be specified as 0-1.

+config MIGRATE_WQ
+ bool "(EXPERIMENTAL) Migrate Workqueues to non-idle cpu"
+ depends on SMP && EXPERIMENTAL
+ help
+ Workqueues queues work on current cpu, if the caller haven't passed a
+ preferred cpu. This may wake up an idle CPU, which is actually not
+ required. This work can be processed by any CPU and so we must select
+ a non-idle CPU here. This patch adds in support in workqueue
+ framework to get preferred CPU details from the scheduler, instead of
+ using current CPU.
+
config HAVE_ARM_SCU
bool
help
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 692a55b..fd8df4a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -456,6 +456,16 @@ static inline void debug_work_activate(struct work_struct *work) { }
static inline void debug_work_deactivate(struct work_struct *work) { }
#endif

+/* This enables migration of a work to a non-IDLE cpu instead of current cpu */
+#ifdef CONFIG_MIGRATE_WQ
+static int wq_select_cpu(void)
+{
+ return sched_select_cpu(SD_NUMA, -1);
+}
+#else
+#define wq_select_cpu() smp_processor_id()
+#endif
+
/* Serializes the accesses to the list of workqueues. */
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
@@ -995,7 +1005,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
struct global_cwq *last_gcwq;

if (unlikely(cpu == WORK_CPU_UNBOUND))
- cpu = raw_smp_processor_id();
+ cpu = wq_select_cpu();

/*
* It's multi cpu. If @wq is non-reentrant and @work
@@ -1066,8 +1076,9 @@ int queue_work(struct workqueue_struct *wq, struct work_struct *work)
{
int ret;

- ret = queue_work_on(get_cpu(), wq, work);
- put_cpu();
+ preempt_disable();
+ ret = queue_work_on(wq_select_cpu(), wq, work);
+ preempt_enable();

return ret;
}
@@ -1102,7 +1113,7 @@ static void delayed_work_timer_fn(unsigned long __data)
struct delayed_work *dwork = (struct delayed_work *)__data;
struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);

- __queue_work(smp_processor_id(), cwq->wq, &dwork->work);
+ __queue_work(wq_select_cpu(), cwq->wq, &dwork->work);
}

/**
@@ -1158,7 +1169,7 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
if (gcwq && gcwq->cpu != WORK_CPU_UNBOUND)
lcpu = gcwq->cpu;
else
- lcpu = raw_smp_processor_id();
+ lcpu = wq_select_cpu();
} else
lcpu = WORK_CPU_UNBOUND;

@@ -2823,8 +2834,8 @@ EXPORT_SYMBOL_GPL(cancel_work_sync);
static inline void __flush_delayed_work(struct delayed_work *dwork)
{
if (del_timer_sync(&dwork->timer))
- __queue_work(raw_smp_processor_id(),
- get_work_cwq(&dwork->work)->wq, &dwork->work);
+ __queue_work(wq_select_cpu(), get_work_cwq(&dwork->work)->wq,
+ &dwork->work);
}

/**
--
1.7.12.rc2.18.g61b472e



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