@@ -318,7 +318,7 @@ static void schedule_tail(struct vcpu *prev)
local_irq_enable();
- context_saved(prev);
+ sched_context_switched(prev, current);
update_runstate_area(current);
@@ -1784,7 +1784,6 @@ static void __context_switch(void)
per_cpu(curr_vcpu, cpu) = n;
}
-
void context_switch(struct vcpu *prev, struct vcpu *next)
{
unsigned int cpu = smp_processor_id();
@@ -1860,7 +1859,7 @@ void context_switch(struct vcpu *prev, struct vcpu *next)
}
}
- context_saved(prev);
+ sched_context_switched(prev, next);
_update_runstate_area(next);
/* Must be done with interrupts enabled */
@@ -59,6 +59,9 @@ boolean_param("sched_smt_power_savings", sched_smt_power_savings);
int sched_ratelimit_us = SCHED_DEFAULT_RATELIMIT_US;
integer_param("sched_ratelimit_us", sched_ratelimit_us);
+/* Number of vcpus per struct sched_unit. */
+static unsigned int __read_mostly sched_granularity = 1;
+
/* Common lock for free cpus. */
static DEFINE_SPINLOCK(sched_free_cpu_lock);
@@ -530,8 +533,8 @@ int sched_move_domain(struct domain *d, struct cpupool *c)
if ( IS_ERR(domdata) )
return PTR_ERR(domdata);
- /* TODO: fix array size with multiple vcpus per unit. */
- unit_priv = xzalloc_array(void *, d->max_vcpus);
+ unit_priv = xzalloc_array(void *,
+ DIV_ROUND_UP(d->max_vcpus, sched_granularity));
if ( unit_priv == NULL )
{
sched_free_domdata(c->sched, domdata);
@@ -1712,133 +1715,325 @@ void vcpu_set_periodic_timer(struct vcpu *v, s_time_t value)
spin_unlock(&v->periodic_timer_lock);
}
-/*
- * The main function
- * - deschedule the current domain (scheduler independent).
- * - pick a new domain (scheduler dependent).
- */
-static void schedule(void)
+static void sched_switch_units(struct sched_resource *sr,
+ struct sched_unit *next, struct sched_unit *prev,
+ s_time_t now)
{
- struct sched_unit *prev = current->sched_unit, *next = NULL;
- s_time_t now;
- struct scheduler *sched;
- unsigned long *tasklet_work = &this_cpu(tasklet_work_to_do);
- bool tasklet_work_scheduled = false;
- struct sched_resource *sd;
- spinlock_t *lock;
- int cpu = smp_processor_id();
+ sr->curr = next;
- ASSERT_NOT_IN_ATOMIC();
+ TRACE_3D(TRC_SCHED_SWITCH_INFPREV, prev->domain->domain_id, prev->unit_id,
+ now - prev->state_entry_time);
+ TRACE_4D(TRC_SCHED_SWITCH_INFNEXT, next->domain->domain_id, next->unit_id,
+ (next->vcpu_list->runstate.state == RUNSTATE_runnable) ?
+ (now - next->state_entry_time) : 0, prev->next_time);
- SCHED_STAT_CRANK(sched_run);
+ ASSERT(prev->vcpu_list->runstate.state == RUNSTATE_running);
+
+ TRACE_4D(TRC_SCHED_SWITCH, prev->domain->domain_id, prev->unit_id,
+ next->domain->domain_id, next->unit_id);
+
+ sched_unit_runstate_change(prev, false, now);
+
+ ASSERT(next->vcpu_list->runstate.state != RUNSTATE_running);
+ sched_unit_runstate_change(next, true, now);
- sd = get_sched_res(cpu);
+ /*
+ * NB. Don't add any trace records from here until the actual context
+ * switch, else lost_records resume will not work properly.
+ */
+
+ ASSERT(!next->is_running);
+ next->vcpu_list->is_running = 1;
+ next->is_running = true;
+ next->state_entry_time = now;
+}
+
+static bool sched_tasklet_check_cpu(unsigned int cpu)
+{
+ unsigned long *tasklet_work = &per_cpu(tasklet_work_to_do, cpu);
- /* Update tasklet scheduling status. */
switch ( *tasklet_work )
{
case TASKLET_enqueued:
set_bit(_TASKLET_scheduled, tasklet_work);
/* fallthrough */
case TASKLET_enqueued|TASKLET_scheduled:
- tasklet_work_scheduled = true;
+ return true;
break;
case TASKLET_scheduled:
clear_bit(_TASKLET_scheduled, tasklet_work);
+ /* fallthrough */
case 0:
- /*tasklet_work_scheduled = false;*/
+ /* return false; */
break;
default:
BUG();
}
- lock = pcpu_schedule_lock_irq(cpu);
+ return false;
+}
- now = NOW();
+static bool sched_tasklet_check(unsigned int cpu)
+{
+ bool tasklet_work_scheduled = false;
+ const cpumask_t *mask = get_sched_res(cpu)->cpus;
+ unsigned int cpu_iter;
+
+ for_each_cpu ( cpu_iter, mask )
+ if ( sched_tasklet_check_cpu(cpu_iter) )
+ tasklet_work_scheduled = true;
- stop_timer(&sd->s_timer);
+ return tasklet_work_scheduled;
+}
+
+static struct sched_unit *do_schedule(struct sched_unit *prev, s_time_t now,
+ unsigned int cpu)
+{
+ struct scheduler *sched = per_cpu(scheduler, cpu);
+ struct sched_resource *sr = get_sched_res(cpu);
+ struct sched_unit *next;
/* get policy-specific decision on scheduling... */
- sched = this_cpu(scheduler);
- sched->do_schedule(sched, prev, now, tasklet_work_scheduled);
+ sched->do_schedule(sched, prev, now, sched_tasklet_check(cpu));
next = prev->next_task;
- sd->curr = next;
-
if ( prev->next_time >= 0 ) /* -ve means no limit */
- set_timer(&sd->s_timer, now + prev->next_time);
+ set_timer(&sr->s_timer, now + prev->next_time);
+
+ if ( likely(prev != next) )
+ sched_switch_units(sr, next, prev, now);
+
+ return next;
+}
+
+static void context_saved(struct vcpu *prev)
+{
+ struct sched_unit *unit = prev->sched_unit;
+
+ /* Clear running flag /after/ writing context to memory. */
+ smp_wmb();
+
+ prev->is_running = 0;
+ unit->is_running = false;
+ unit->state_entry_time = NOW();
+
+ /* Check for migration request /after/ clearing running flag. */
+ smp_mb();
+
+ sched_context_saved(vcpu_scheduler(prev), unit);
- if ( unlikely(prev == next) )
+ sched_unit_migrate_finish(unit);
+}
+
+/*
+ * Rendezvous on end of context switch.
+ * As no lock is protecting this rendezvous function we need to use atomic
+ * access functions on the counter.
+ * The counter will be 0 in case no rendezvous is needed. For the rendezvous
+ * case it is initialised to the number of cpus to rendezvous plus 1. Each
+ * member entering decrements the counter. The last one will decrement it to
+ * 1 and perform the final needed action in that case (call of context_saved()
+ * if vcpu was switched), and then set the counter to zero. The other members
+ * will wait until the counter becomes zero until they proceed.
+ */
+void sched_context_switched(struct vcpu *vprev, struct vcpu *vnext)
+{
+ struct sched_unit *next = vnext->sched_unit;
+
+ if ( atomic_read(&next->rendezvous_out_cnt) )
+ {
+ int cnt = atomic_dec_return(&next->rendezvous_out_cnt);
+
+ /* Call context_saved() before releasing other waiters. */
+ if ( cnt == 1 )
+ {
+ if ( vprev != vnext )
+ context_saved(vprev);
+ atomic_set(&next->rendezvous_out_cnt, 0);
+ }
+ else
+ while ( atomic_read(&next->rendezvous_out_cnt) )
+ cpu_relax();
+ }
+ else if ( vprev != vnext )
+ context_saved(vprev);
+}
+
+static void sched_context_switch(struct vcpu *vprev, struct vcpu *vnext,
+ s_time_t now)
+{
+ if ( unlikely(vprev == vnext) )
{
- pcpu_schedule_unlock_irq(lock, cpu);
TRACE_4D(TRC_SCHED_SWITCH_INFCONT,
- next->domain->domain_id, next->unit_id,
- now - prev->state_entry_time,
- prev->next_time);
- trace_continue_running(next->vcpu_list);
- return continue_running(prev->vcpu_list);
+ vnext->domain->domain_id, vnext->sched_unit->unit_id,
+ now - vprev->runstate.state_entry_time,
+ vprev->sched_unit->next_time);
+ sched_context_switched(vprev, vnext);
+ trace_continue_running(vnext);
+ return continue_running(vprev);
}
- TRACE_3D(TRC_SCHED_SWITCH_INFPREV,
- prev->domain->domain_id, prev->unit_id,
- now - prev->state_entry_time);
- TRACE_4D(TRC_SCHED_SWITCH_INFNEXT,
- next->domain->domain_id, next->unit_id,
- (next->vcpu_list->runstate.state == RUNSTATE_runnable) ?
- (now - next->state_entry_time) : 0,
- prev->next_time);
+ SCHED_STAT_CRANK(sched_ctx);
- ASSERT(prev->vcpu_list->runstate.state == RUNSTATE_running);
+ stop_timer(&vprev->periodic_timer);
- TRACE_4D(TRC_SCHED_SWITCH,
- prev->domain->domain_id, prev->unit_id,
- next->domain->domain_id, next->unit_id);
+ if ( vnext->sched_unit->migrated )
+ vcpu_move_irqs(vnext);
- sched_unit_runstate_change(prev, false, now);
+ vcpu_periodic_timer_work(vnext);
- ASSERT(next->vcpu_list->runstate.state != RUNSTATE_running);
- sched_unit_runstate_change(next, true, now);
+ context_switch(vprev, vnext);
+}
- /*
- * NB. Don't add any trace records from here until the actual context
- * switch, else lost_records resume will not work properly.
- */
+/*
+ * Rendezvous before taking a scheduling decision.
+ * Called with schedule lock held, so all accesses to the rendezvous counter
+ * can be normal ones (no atomic accesses needed).
+ * The counter is initialized to the number of cpus to rendezvous initially.
+ * Each cpu entering will decrement the counter. In case the counter becomes
+ * zero do_schedule() is called and the rendezvous counter for leaving
+ * context_switch() is set. All other members will wait until the counter is
+ * becoming zero, dropping the schedule lock in between.
+ */
+static struct sched_unit *sched_wait_rendezvous_in(struct sched_unit *prev,
+ spinlock_t **lock, int cpu,
+ s_time_t now)
+{
+ struct sched_unit *next;
- ASSERT(!next->is_running);
- next->vcpu_list->is_running = 1;
- next->is_running = true;
- next->state_entry_time = now;
+ if ( !--prev->rendezvous_in_cnt )
+ {
+ next = do_schedule(prev, now, cpu);
+ atomic_set(&next->rendezvous_out_cnt, sched_granularity + 1);
+ return next;
+ }
- pcpu_schedule_unlock_irq(lock, cpu);
+ while ( prev->rendezvous_in_cnt )
+ {
+ /*
+ * Coming from idle might need to do tasklet work.
+ * In order to avoid deadlocks we can't do that here, but have to
+ * continue the idle loop.
+ * Undo the rendezvous_in_cnt decrement and schedule another call of
+ * sched_slave().
+ */
+ if ( is_idle_unit(prev) && sched_tasklet_check_cpu(cpu) )
+ {
+ struct vcpu *vprev = current;
- SCHED_STAT_CRANK(sched_ctx);
+ prev->rendezvous_in_cnt++;
+ atomic_set(&prev->rendezvous_out_cnt, 0);
+
+ pcpu_schedule_unlock_irq(*lock, cpu);
+
+ raise_softirq(SCHED_SLAVE_SOFTIRQ);
+ sched_context_switch(vprev, vprev, now);
+
+ return NULL; /* ARM only. */
+ }
- stop_timer(&prev->vcpu_list->periodic_timer);
+ pcpu_schedule_unlock_irq(*lock, cpu);
- if ( next->migrated )
- vcpu_move_irqs(next->vcpu_list);
+ cpu_relax();
- vcpu_periodic_timer_work(next->vcpu_list);
+ *lock = pcpu_schedule_lock_irq(cpu);
+ }
- context_switch(prev->vcpu_list, next->vcpu_list);
+ return prev->next_task;
}
-void context_saved(struct vcpu *prev)
+static void sched_slave(void)
{
- /* Clear running flag /after/ writing context to memory. */
- smp_wmb();
+ struct vcpu *vprev = current;
+ struct sched_unit *prev = vprev->sched_unit, *next;
+ s_time_t now;
+ spinlock_t *lock;
+ unsigned int cpu = smp_processor_id();
- prev->is_running = 0;
- prev->sched_unit->is_running = false;
- prev->sched_unit->state_entry_time = NOW();
+ ASSERT_NOT_IN_ATOMIC();
- /* Check for migration request /after/ clearing running flag. */
- smp_mb();
+ lock = pcpu_schedule_lock_irq(cpu);
- sched_context_saved(vcpu_scheduler(prev), prev->sched_unit);
+ now = NOW();
+
+ if ( !prev->rendezvous_in_cnt )
+ {
+ pcpu_schedule_unlock_irq(lock, cpu);
+ return;
+ }
+
+ stop_timer(&get_sched_res(cpu)->s_timer);
+
+ next = sched_wait_rendezvous_in(prev, &lock, cpu, now);
+ if ( !next )
+ return;
+
+ pcpu_schedule_unlock_irq(lock, cpu);
- sched_unit_migrate_finish(prev->sched_unit);
+ sched_context_switch(vprev, next->vcpu_list, now);
+}
+
+/*
+ * The main function
+ * - deschedule the current domain (scheduler independent).
+ * - pick a new domain (scheduler dependent).
+ */
+static void schedule(void)
+{
+ struct vcpu *vnext, *vprev = current;
+ struct sched_unit *prev = vprev->sched_unit, *next = NULL;
+ s_time_t now;
+ struct sched_resource *sr;
+ spinlock_t *lock;
+ int cpu = smp_processor_id();
+
+ ASSERT_NOT_IN_ATOMIC();
+
+ SCHED_STAT_CRANK(sched_run);
+
+ sr = get_sched_res(cpu);
+
+ lock = pcpu_schedule_lock_irq(cpu);
+
+ if ( prev->rendezvous_in_cnt )
+ {
+ /*
+ * We have a race: sched_slave() should be called, so raise a softirq
+ * in order to re-enter schedule() later and call sched_slave() now.
+ */
+ pcpu_schedule_unlock_irq(lock, cpu);
+
+ raise_softirq(SCHEDULE_SOFTIRQ);
+ return sched_slave();
+ }
+
+ stop_timer(&sr->s_timer);
+
+ now = NOW();
+
+ if ( sched_granularity > 1 )
+ {
+ cpumask_t mask;
+
+ prev->rendezvous_in_cnt = sched_granularity;
+ cpumask_andnot(&mask, sr->cpus, cpumask_of(cpu));
+ cpumask_raise_softirq(&mask, SCHED_SLAVE_SOFTIRQ);
+ next = sched_wait_rendezvous_in(prev, &lock, cpu, now);
+ if ( !next )
+ return;
+ }
+ else
+ {
+ prev->rendezvous_in_cnt = 0;
+ next = do_schedule(prev, now, cpu);
+ atomic_set(&next->rendezvous_out_cnt, 0);
+ }
+
+ pcpu_schedule_unlock_irq(lock, cpu);
+
+ vnext = next->vcpu_list;
+ sched_context_switch(vprev, vnext, now);
}
/* The scheduler timer: force a run through the scheduler */
@@ -1879,6 +2074,7 @@ static int cpu_schedule_up(unsigned int cpu)
if ( sr == NULL )
return -ENOMEM;
sr->master_cpu = cpu;
+ sr->cpus = cpumask_of(cpu);
set_sched_res(cpu, sr);
per_cpu(scheduler, cpu) = &sched_idle_ops;
@@ -1899,6 +2095,8 @@ static int cpu_schedule_up(unsigned int cpu)
if ( idle_vcpu[cpu] == NULL )
return -ENOMEM;
+ idle_vcpu[cpu]->sched_unit->rendezvous_in_cnt = 0;
+
/*
* No need to allocate any scheduler data, as cpus coming online are
* free initially and the idle scheduler doesn't need any data areas
@@ -1999,6 +2197,7 @@ void __init scheduler_init(void)
int i;
open_softirq(SCHEDULE_SOFTIRQ, schedule);
+ open_softirq(SCHED_SLAVE_SOFTIRQ, sched_slave);
for ( i = 0; i < NUM_SCHEDULERS; i++)
{
@@ -33,8 +33,8 @@ static void __do_softirq(unsigned long ignore_mask)
for ( ; ; )
{
/*
- * Initialise @cpu on every iteration: SCHEDULE_SOFTIRQ may move
- * us to another processor.
+ * Initialise @cpu on every iteration: SCHEDULE_SOFTIRQ or
+ * SCHED_SLAVE_SOFTIRQ may move us to another processor.
*/
cpu = smp_processor_id();
@@ -55,7 +55,7 @@ void process_pending_softirqs(void)
{
ASSERT(!in_irq() && local_irq_is_enabled());
/* Do not enter scheduler as it can preempt the calling context. */
- __do_softirq(1ul<<SCHEDULE_SOFTIRQ);
+ __do_softirq((1ul << SCHEDULE_SOFTIRQ) | (1ul << SCHED_SLAVE_SOFTIRQ));
}
void do_softirq(void)
@@ -42,6 +42,7 @@ struct sched_resource {
/* Cpu with lowest id in scheduling resource. */
unsigned int master_cpu;
+ const cpumask_t *cpus; /* cpus covered by this struct */
};
DECLARE_PER_CPU(struct scheduler *, scheduler);
@@ -292,6 +292,12 @@ struct sched_unit {
/* Next unit to run. */
struct sched_unit *next_task;
s_time_t next_time;
+
+ /* Number of vcpus not yet joined for context switch. */
+ unsigned int rendezvous_in_cnt;
+
+ /* Number of vcpus not yet finished with context switch. */
+ atomic_t rendezvous_out_cnt;
};
#define for_each_sched_unit(d, u) \
@@ -696,10 +702,10 @@ void sync_local_execstate(void);
/*
* Called by the scheduler to switch to another VCPU. This function must
- * call context_saved(@prev) when the local CPU is no longer running in
- * @prev's context, and that context is saved to memory. Alternatively, if
- * implementing lazy context switching, it suffices to ensure that invoking
- * sync_vcpu_execstate() will switch and commit @prev's state.
+ * call sched_context_switched(@prev, @next) when the local CPU is no longer
+ * running in @prev's context, and that context is saved to memory.
+ * Alternatively, if implementing lazy context switching, it suffices to ensure
+ * that invoking sync_vcpu_execstate() will switch and commit @prev's state.
*/
void context_switch(
struct vcpu *prev,
@@ -711,7 +717,7 @@ void context_switch(
* saved to memory. Alternatively, if implementing lazy context switching,
* ensure that invoking sync_vcpu_execstate() will switch and commit @prev.
*/
-void context_saved(struct vcpu *prev);
+void sched_context_switched(struct vcpu *prev, struct vcpu *vnext);
/* Called by the scheduler to continue running the current VCPU. */
void continue_running(
@@ -4,6 +4,7 @@
/* Low-latency softirqs come first in the following list. */
enum {
TIMER_SOFTIRQ = 0,
+ SCHED_SLAVE_SOFTIRQ,
SCHEDULE_SOFTIRQ,
NEW_TLBFLUSH_CLOCK_PERIOD_SOFTIRQ,
RCU_SOFTIRQ,
When switching sched units synchronize all vcpus of the new unit to be scheduled at the same time. A variable sched_granularity is added which holds the number of vcpus per schedule unit. As tasklets require to schedule the idle unit it is required to set the tasklet_work_scheduled parameter of do_schedule() to true if any cpu covered by the current schedule() call has any pending tasklet work. For joining other vcpus of the schedule unit we need to add a new softirq SCHED_SLAVE_SOFTIRQ in order to have a way to initiate a context switch without calling the generic schedule() function selecting the vcpu to switch to, as we already know which vcpu we want to run. This has the other advantage not to loose any other concurrent SCHEDULE_SOFTIRQ events. Signed-off-by: Juergen Gross <jgross@suse.com> --- RFC V2: - move syncing after context_switch() to schedule.c V2: - don't run tasklets directly from sched_wait_rendezvous_in() V3: - adapt array size in sched_move_domain() (Jan Beulich) - int -> unsigned int (Jan Beulich) V4: - renamed sd to sr in several places (Jan Beulich) - swap stop_timer() and NOW() calls (Jan Beulich) - context_switch() on ARM returns - handle that (Jan Beulich) --- xen/arch/arm/domain.c | 2 +- xen/arch/x86/domain.c | 3 +- xen/common/schedule.c | 353 +++++++++++++++++++++++++++++++++++---------- xen/common/softirq.c | 6 +- xen/include/xen/sched-if.h | 1 + xen/include/xen/sched.h | 16 +- xen/include/xen/softirq.h | 1 + 7 files changed, 294 insertions(+), 88 deletions(-)