[Xen-devel] [PATCH v2 47/48] xen/sched: disable scheduling when entering ACPI deep sleep states

[Juergen Gross <jgross@xxxxxxxx>]

When entering deep sleep states all domains are paused resulting in
all cpus only running idle vcpus. This enables us to stop scheduling
completely in order to avoid synchronization problems with core
scheduling when individual cpus are offlined.

Disabling the scheduler is done by replacing the softirq handler
with a dummy scheduling routine only enabling tasklets to run.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2: new patch
---
 xen/arch/x86/acpi/power.c |  4 ++++
 xen/common/schedule.c     | 31 +++++++++++++++++++++++++++++--
 xen/include/xen/sched.h   |  2 ++
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
index aecc754fdb..431db8dca8 100644
--- a/xen/arch/x86/acpi/power.c
+++ b/xen/arch/x86/acpi/power.c
@@ -122,12 +122,16 @@ static void freeze_domains(void)
     for_each_domain ( d )
         domain_pause(d);
     rcu_read_unlock(&domlist_read_lock);
+
+    scheduler_disable();
 }
 
 static void thaw_domains(void)
 {
     struct domain *d;
 
+    scheduler_enable();
+
     rcu_read_lock(&domlist_read_lock);
     for_each_domain ( d )
     {
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index e0521de8ce..181adb00b2 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -84,6 +84,8 @@ extern const struct scheduler *__start_schedulers_array[], 
*__end_schedulers_arr
 
 static struct scheduler __read_mostly ops;
 
+static bool scheduler_active;
+
 static struct sched_resource *
 sched_idle_res_pick(const struct scheduler *ops, struct sched_unit *unit)
 {
@@ -2230,6 +2232,13 @@ static struct sched_unit 
*sched_wait_rendezvous_in(struct sched_unit *prev,
         cpu_relax();
 
         *lock = pcpu_schedule_lock_irq(cpu);
+
+        if ( unlikely(!scheduler_active) )
+        {
+            ASSERT(is_idle_unit(prev));
+            atomic_set(&prev->next_task->rendezvous_out_cnt, 0);
+            prev->rendezvous_in_cnt = 0;
+        }
     }
 
     return prev->next_task;
@@ -2578,14 +2587,32 @@ const cpumask_t *sched_get_opt_cpumask(enum sched_gran 
opt, unsigned int cpu)
     return mask;
 }
 
+static void schedule_dummy(void)
+{
+    sched_tasklet_check_cpu(smp_processor_id());
+}
+
+void scheduler_disable(void)
+{
+    scheduler_active = false;
+    open_softirq(SCHEDULE_SOFTIRQ, schedule_dummy);
+    open_softirq(SCHED_SLAVE_SOFTIRQ, schedule_dummy);
+}
+
+void scheduler_enable(void)
+{
+    open_softirq(SCHEDULE_SOFTIRQ, schedule);
+    open_softirq(SCHED_SLAVE_SOFTIRQ, sched_slave);
+    scheduler_active = true;
+}
+
 /* Initialise the data structures. */
 void __init scheduler_init(void)
 {
     struct domain *idle_domain;
     int i;
 
-    open_softirq(SCHEDULE_SOFTIRQ, schedule);
-    open_softirq(SCHED_SLAVE_SOFTIRQ, sched_slave);
+    scheduler_enable();
 
     for ( i = 0; i < NUM_SCHEDULERS; i++)
     {
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 346e564e05..6d0ea1f60b 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -926,6 +926,8 @@ void vcpu_runstate_get(struct vcpu *v, struct 
vcpu_runstate_info *runstate);
 uint64_t get_cpu_idle_time(unsigned int cpu);
 bool sched_has_urgent_vcpu(void);
 void sched_guest_idle(void (*idle) (void), unsigned int cpu);
+void scheduler_enable(void);
+void scheduler_disable(void);
 
 /*
  * Used by idle loop to decide whether there is work to do:
-- 
2.16.4


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