@@ -1709,12 +1709,45 @@ static void __context_switch(void)
per_cpu(curr_vcpu, cpu) = n;
}
+/*
+ * 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 prev was specified, and then set the counter to zero. The other members
+ * will wait until the counter becomes zero until they proceed.
+ */
+static void context_wait_rendezvous_out(struct sched_item *item,
+ struct vcpu *prev)
+{
+ if ( atomic_read(&item->rendezvous_out_cnt) )
+ {
+ int cnt = atomic_dec_return(&item->rendezvous_out_cnt);
+
+ /* Call context_saved() before releasing other waiters. */
+ if ( cnt == 1 )
+ {
+ if ( prev )
+ context_saved(prev);
+ atomic_set(&item->rendezvous_out_cnt, 0);
+ }
+ else
+ while ( atomic_read(&item->rendezvous_out_cnt) )
+ cpu_relax();
+ }
+ else if ( prev )
+ context_saved(prev);
+}
void context_switch(struct vcpu *prev, struct vcpu *next)
{
unsigned int cpu = smp_processor_id();
const struct domain *prevd = prev->domain, *nextd = next->domain;
unsigned int dirty_cpu = next->dirty_cpu;
+ struct sched_item *item = next->sched_item;
ASSERT(local_irq_is_enabled());
@@ -1787,7 +1820,7 @@ void context_switch(struct vcpu *prev, struct vcpu *next)
}
}
- context_saved(prev);
+ context_wait_rendezvous_out(item, prev);
if ( prev != next )
{
@@ -1812,6 +1845,8 @@ void context_switch(struct vcpu *prev, struct vcpu *next)
void continue_running(struct vcpu *same)
{
+ context_wait_rendezvous_out(same->sched_item, NULL);
+
/* See the comment above. */
same->domain->arch.ctxt_switch->tail(same);
BUG();
@@ -54,6 +54,10 @@ 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_item. */
+static unsigned int sched_granularity = 1;
+
/* Various timer handlers. */
static void s_timer_fn(void *unused);
static void vcpu_periodic_timer_fn(void *data);
@@ -1600,116 +1604,235 @@ static void vcpu_periodic_timer_work(struct vcpu *v)
set_timer(&v->periodic_timer, periodic_next_event);
}
-/*
- * The main function
- * - deschedule the current domain (scheduler independent).
- * - pick a new domain (scheduler dependent).
- */
-static void schedule(void)
+static void sched_switch_items(struct sched_resource *sd,
+ struct sched_item *next, struct sched_item *prev,
+ s_time_t now)
{
- struct sched_item *prev = current->sched_item, *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();
+ sd->curr = next;
- ASSERT_NOT_IN_ATOMIC();
+ TRACE_3D(TRC_SCHED_SWITCH_INFPREV, prev->domain->domain_id, prev->item_id,
+ now - prev->state_entry_time);
+ TRACE_4D(TRC_SCHED_SWITCH_INFNEXT, next->domain->domain_id, next->item_id,
+ (next->vcpu->runstate.state == RUNSTATE_runnable) ?
+ (now - next->state_entry_time) : 0, prev->next_time);
- SCHED_STAT_CRANK(sched_run);
+ ASSERT(prev->vcpu->runstate.state == RUNSTATE_running);
- sd = this_cpu(sched_res);
+ TRACE_4D(TRC_SCHED_SWITCH, prev->domain->domain_id, prev->item_id,
+ next->domain->domain_id, next->item_id);
+
+ sched_item_runstate_change(prev, false, now);
+ prev->last_run_time = now;
+
+ ASSERT(next->vcpu->runstate.state != RUNSTATE_running);
+ sched_item_runstate_change(next, true, now);
+
+ /*
+ * 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->is_running = 1;
+}
+
+static bool sched_tasklet_check(void)
+{
+ unsigned long *tasklet_work;
+ bool tasklet_work_scheduled = false;
+ const cpumask_t *mask = this_cpu(sched_res)->cpus;
+ int cpu;
- /* Update tasklet scheduling status. */
- switch ( *tasklet_work )
+ for_each_cpu ( cpu, mask )
{
- case TASKLET_enqueued:
- set_bit(_TASKLET_scheduled, tasklet_work);
- /* fallthrough */
- case TASKLET_enqueued|TASKLET_scheduled:
- tasklet_work_scheduled = true;
- break;
- case TASKLET_scheduled:
- clear_bit(_TASKLET_scheduled, tasklet_work);
- case 0:
- /*tasklet_work_scheduled = false;*/
- break;
- default:
- BUG();
- }
+ tasklet_work = &per_cpu(tasklet_work_to_do, cpu);
- lock = pcpu_schedule_lock_irq(cpu);
+ switch ( *tasklet_work )
+ {
+ case TASKLET_enqueued:
+ set_bit(_TASKLET_scheduled, tasklet_work);
+ /* fallthrough */
+ case TASKLET_enqueued|TASKLET_scheduled:
+ tasklet_work_scheduled = true;
+ break;
+ case TASKLET_scheduled:
+ clear_bit(_TASKLET_scheduled, tasklet_work);
+ case 0:
+ /*tasklet_work_scheduled = false;*/
+ break;
+ default:
+ BUG();
+ }
+ }
- now = NOW();
+ return tasklet_work_scheduled;
+}
- stop_timer(&sd->s_timer);
+static struct sched_item *do_schedule(struct sched_item *prev, s_time_t now)
+{
+ struct scheduler *sched = this_cpu(scheduler);
+ struct sched_resource *sd = this_cpu(sched_res);
+ struct sched_item *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());
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);
- if ( unlikely(prev == next) )
+ if ( likely(prev != next) )
+ sched_switch_items(sd, next, prev, now);
+
+ return next;
+}
+
+/*
+ * 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_item *sched_wait_rendezvous_in(struct sched_item *prev,
+ spinlock_t *lock, int cpu,
+ s_time_t now)
+{
+ struct sched_item *next;
+
+ if ( !--prev->rendezvous_in_cnt )
+ {
+ next = do_schedule(prev, now);
+ atomic_set(&next->rendezvous_out_cnt, sched_granularity + 1);
+ return next;
+ }
+
+ while ( prev->rendezvous_in_cnt )
{
pcpu_schedule_unlock_irq(lock, cpu);
+ cpu_relax();
+ pcpu_schedule_lock_irq(cpu);
+ }
+
+ return prev->next_task;
+}
+
+static void sched_context_switch(struct vcpu *vprev, struct vcpu *vnext,
+ s_time_t now)
+{
+ if ( unlikely(vprev == vnext) )
+ {
TRACE_4D(TRC_SCHED_SWITCH_INFCONT,
- next->domain->domain_id, next->item_id,
- now - prev->state_entry_time,
- prev->next_time);
- trace_continue_running(next->vcpu);
- return continue_running(prev->vcpu);
+ vnext->domain->domain_id, vnext->sched_item->item_id,
+ now - vprev->runstate.state_entry_time,
+ vprev->sched_item->next_time);
+ trace_continue_running(vnext);
+ return continue_running(vprev);
}
- TRACE_3D(TRC_SCHED_SWITCH_INFPREV,
- prev->domain->domain_id, prev->item_id,
- now - prev->state_entry_time);
- TRACE_4D(TRC_SCHED_SWITCH_INFNEXT,
- next->domain->domain_id, next->item_id,
- (next->vcpu->runstate.state == RUNSTATE_runnable) ?
- (now - next->state_entry_time) : 0,
- prev->next_time);
+ SCHED_STAT_CRANK(sched_ctx);
- ASSERT(prev->vcpu->runstate.state == RUNSTATE_running);
+ stop_timer(&vprev->periodic_timer);
- TRACE_4D(TRC_SCHED_SWITCH,
- prev->domain->domain_id, prev->item_id,
- next->domain->domain_id, next->item_id);
+ if ( vnext->sched_item->migrated )
+ vcpu_move_irqs(vnext);
- sched_item_runstate_change(prev, false, now);
- prev->last_run_time = now;
+ vcpu_periodic_timer_work(vnext);
- ASSERT(next->vcpu->runstate.state != RUNSTATE_running);
- sched_item_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.
- */
+static void sched_slave(void)
+{
+ struct vcpu *vprev = current;
+ struct sched_item *prev = vprev->sched_item, *next;
+ s_time_t now;
+ spinlock_t *lock;
+ int cpu = smp_processor_id();
- ASSERT(!next->is_running);
- next->is_running = 1;
- next->state_entry_time = now;
+ ASSERT_NOT_IN_ATOMIC();
+
+ lock = pcpu_schedule_lock_irq(cpu);
+
+ now = NOW();
+
+ if ( !prev->rendezvous_in_cnt )
+ {
+ pcpu_schedule_unlock_irq(lock, cpu);
+ return;
+ }
+
+ stop_timer(&this_cpu(sched_res)->s_timer);
+
+ next = sched_wait_rendezvous_in(prev, lock, cpu, now);
pcpu_schedule_unlock_irq(lock, cpu);
- SCHED_STAT_CRANK(sched_ctx);
+ sched_context_switch(vprev, next->vcpu, now);
+}
- stop_timer(&prev->vcpu->periodic_timer);
+/*
+ * 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_item *prev = vprev->sched_item, *next = NULL;
+ s_time_t now;
+ struct sched_resource *sd;
+ spinlock_t *lock;
+ int cpu = smp_processor_id();
+
+ ASSERT_NOT_IN_ATOMIC();
- if ( next->migrated )
- vcpu_move_irqs(next->vcpu);
+ SCHED_STAT_CRANK(sched_run);
- vcpu_periodic_timer_work(next->vcpu);
+ sd = this_cpu(sched_res);
+
+ 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();
+ }
+
+ now = NOW();
+
+ stop_timer(&sd->s_timer);
+
+ if ( sched_granularity > 1 )
+ {
+ cpumask_t mask;
+
+ prev->rendezvous_in_cnt = sched_granularity;
+ cpumask_andnot(&mask, sd->cpus, cpumask_of(cpu));
+ cpumask_raise_softirq(&mask, SCHED_SLAVE_SOFTIRQ);
+ next = sched_wait_rendezvous_in(prev, lock, cpu, now);
+ }
+ else
+ {
+ prev->rendezvous_in_cnt = 0;
+ next = do_schedule(prev, now);
+ atomic_set(&next->rendezvous_out_cnt, 0);
+ }
+
+ pcpu_schedule_unlock_irq(lock, cpu);
- context_switch(prev->vcpu, next->vcpu);
+ vnext = next->vcpu;
+ sched_context_switch(vprev, vnext, now);
}
void context_saved(struct vcpu *prev)
@@ -1767,6 +1890,7 @@ static int cpu_schedule_up(unsigned int cpu)
if ( sd == NULL )
return -ENOMEM;
sd->processor = cpu;
+ sd->cpus = cpumask_of(cpu);
per_cpu(sched_res, cpu) = sd;
per_cpu(scheduler, cpu) = &ops;
@@ -1926,6 +2050,7 @@ 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)
@@ -41,6 +41,7 @@ struct sched_resource {
struct timer s_timer; /* scheduling timer */
atomic_t urgent_count; /* how many urgent vcpus */
unsigned processor;
+ const cpumask_t *cpus; /* cpus covered by this struct */
};
#define curr_on_cpu(c) (per_cpu(sched_res, c)->curr)
@@ -86,6 +87,12 @@ struct sched_item {
/* Next item to run. */
struct sched_item *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_item(d, e) \
@@ -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 items synchronize all vcpus of the new item to be scheduled at the same time. A variable sched_granularity is added which holds the number of vcpus per schedule item. As tasklets require to schedule the idle item 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 item 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> --- xen/arch/x86/domain.c | 37 +++++- xen/common/schedule.c | 275 ++++++++++++++++++++++++++++++++------------- xen/common/softirq.c | 6 +- xen/include/xen/sched-if.h | 7 ++ xen/include/xen/softirq.h | 1 + 5 files changed, 247 insertions(+), 79 deletions(-)