[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH RFC V2 43/45] xen/sched: make vcpu_wake() and vcpu_sleep() core scheduling aware
vcpu_wake() and vcpu_sleep() need to be made core scheduling aware: they might need to switch a single vcpu of an already scheduled item between running and not running. Especially when vcpu_sleep() for a vcpu is being called by a vcpu of the same scheduling item special care must be taken in order to avoid a deadlock: the vcpu to be put asleep must be forced through a context switch without doing so for the calling vcpu. For this purpose add a vcpu flag handled in sched_slave() and in sched_wait_rendezvous_in() allowing a vcpu of the currently running item to switch state at a higher priority than a normal schedule event. Use the same mechanism when waking up a vcpu of a currently active item. While at it make vcpu_sleep_nosync_locked() static as it is used in schedule.c only. Signed-off-by: Juergen Gross <jgross@xxxxxxxx> --- RFC V2: add vcpu_sleep() handling and force_context_switch flag --- xen/common/schedule.c | 144 ++++++++++++++++++++++++++++++++++++++++----- xen/include/xen/sched-if.h | 9 ++- xen/include/xen/sched.h | 2 + 3 files changed, 136 insertions(+), 19 deletions(-) diff --git a/xen/common/schedule.c b/xen/common/schedule.c index 788ecc9e81..49ed2b5900 100644 --- a/xen/common/schedule.c +++ b/xen/common/schedule.c @@ -79,21 +79,21 @@ extern const struct scheduler *__start_schedulers_array[], *__end_schedulers_arr static struct scheduler __read_mostly ops; -static inline struct vcpu *sched_item2vcpu_cpu(struct sched_item *item, - unsigned int cpu) +static inline struct vcpu *item2vcpu_cpu(struct sched_item *item, + unsigned int cpu) { unsigned int idx = item->item_id + per_cpu(sched_res_idx, cpu); const struct domain *d = item->domain; - struct vcpu *v; - if ( idx < d->max_vcpus && d->vcpu[idx] ) - { - v = d->vcpu[idx]; - if ( v->new_state == RUNSTATE_running ) - return v; - } + return (idx < d->max_vcpus && d->vcpu[idx]) ? d->vcpu[idx] : NULL; +} - return idle_vcpu[cpu]; +static inline struct vcpu *sched_item2vcpu_cpu(struct sched_item *item, + unsigned int cpu) +{ + struct vcpu *v = item2vcpu_cpu(item, cpu); + + return (v && v->new_state == RUNSTATE_running) ? v : idle_vcpu[cpu]; } static inline struct scheduler *dom_scheduler(const struct domain *d) @@ -644,8 +644,10 @@ void sched_destroy_domain(struct domain *d) } } -void vcpu_sleep_nosync_locked(struct vcpu *v) +static void vcpu_sleep_nosync_locked(struct vcpu *v) { + struct sched_item *item = v->sched_item; + ASSERT(spin_is_locked(per_cpu(sched_res, v->processor)->schedule_lock)); if ( likely(!vcpu_runnable(v)) ) @@ -653,7 +655,14 @@ void vcpu_sleep_nosync_locked(struct vcpu *v) if ( v->runstate.state == RUNSTATE_runnable ) vcpu_runstate_change(v, RUNSTATE_offline, NOW()); - sched_sleep(vcpu_scheduler(v), v->sched_item); + if ( likely(!item_runnable(item)) ) + sched_sleep(vcpu_scheduler(v), item); + else if ( item_running(item) > 1 && v->is_running && + !v->force_context_switch ) + { + v->force_context_switch = true; + cpu_raise_softirq(v->processor, SCHED_SLAVE_SOFTIRQ); + } } } @@ -685,16 +694,22 @@ void vcpu_wake(struct vcpu *v) { unsigned long flags; spinlock_t *lock; + struct sched_item *item = v->sched_item; TRACE_2D(TRC_SCHED_WAKE, v->domain->domain_id, v->vcpu_id); - lock = item_schedule_lock_irqsave(v->sched_item, &flags); + lock = item_schedule_lock_irqsave(item, &flags); if ( likely(vcpu_runnable(v)) ) { if ( v->runstate.state >= RUNSTATE_blocked ) vcpu_runstate_change(v, RUNSTATE_runnable, NOW()); - sched_wake(vcpu_scheduler(v), v->sched_item); + sched_wake(vcpu_scheduler(v), item); + if ( item->is_running && !v->is_running && !v->force_context_switch ) + { + v->force_context_switch = true; + cpu_raise_softirq(v->processor, SCHED_SLAVE_SOFTIRQ); + } } else if ( !(v->pause_flags & VPF_blocked) ) { @@ -702,7 +717,7 @@ void vcpu_wake(struct vcpu *v) vcpu_runstate_change(v, RUNSTATE_offline, NOW()); } - item_schedule_unlock_irqrestore(lock, flags, v->sched_item); + item_schedule_unlock_irqrestore(lock, flags, item); } void vcpu_unblock(struct vcpu *v) @@ -1835,6 +1850,61 @@ static void sched_context_switch(struct vcpu *vprev, struct vcpu *vnext, context_switch(vprev, vnext); } +/* + * Force a context switch of a single vcpu of an item. + * Might be called either if a vcpu of an already running item is woken up + * or if a vcpu of a running item is put asleep with other vcpus of the same + * item still running. + */ +static struct vcpu *sched_force_context_switch(struct vcpu *vprev, + struct vcpu *v, + int cpu, s_time_t now) +{ + v->force_context_switch = false; + + if ( vcpu_runnable(v) == v->is_running ) + return NULL; + + if ( vcpu_runnable(v) ) + { + if ( is_idle_vcpu(vprev) ) + { + vcpu_runstate_change(vprev, RUNSTATE_runnable, now); + vprev->sched_item = this_cpu(sched_res)->sched_item_idle; + } + vcpu_runstate_change(v, RUNSTATE_running, now); + } + else + { + /* Make sure not to switch last vcpu of an item away. */ + if ( item_running(v->sched_item) == 1 ) + return NULL; + + vcpu_runstate_change(v, vcpu_runstate_blocked(v), now); + v = sched_item2vcpu_cpu(vprev->sched_item, cpu); + if ( v != vprev ) + { + if ( is_idle_vcpu(vprev) ) + { + vcpu_runstate_change(vprev, RUNSTATE_runnable, now); + vprev->sched_item = this_cpu(sched_res)->sched_item_idle; + } + else + { + v->sched_item = vprev->sched_item; + vcpu_runstate_change(v, RUNSTATE_running, now); + } + } + } + + v->is_running = 1; + + /* Make sure not to loose another slave call. */ + raise_softirq(SCHED_SLAVE_SOFTIRQ); + + return v; +} + /* * Rendezvous before taking a scheduling decision. * Called with schedule lock held, so all accesses to the rendezvous counter @@ -1850,6 +1920,7 @@ static struct sched_item *sched_wait_rendezvous_in(struct sched_item *prev, s_time_t now) { struct sched_item *next; + struct vcpu *v; if ( !--prev->rendezvous_in_cnt ) { @@ -1858,8 +1929,28 @@ static struct sched_item *sched_wait_rendezvous_in(struct sched_item *prev, return next; } + v = item2vcpu_cpu(prev, cpu); while ( prev->rendezvous_in_cnt ) { + if ( v && v->force_context_switch ) + { + struct vcpu *vprev = current; + + v = sched_force_context_switch(vprev, v, cpu, now); + + if ( v ) + { + /* We'll come back another time, so adjust rendezvous_in_cnt. */ + prev->rendezvous_in_cnt++; + + pcpu_schedule_unlock_irq(lock, cpu); + + sched_context_switch(vprev, v, false, now); + } + + v = item2vcpu_cpu(prev, cpu); + } + pcpu_schedule_unlock_irq(lock, cpu); cpu_relax(); pcpu_schedule_lock_irq(cpu); @@ -1870,10 +1961,11 @@ static struct sched_item *sched_wait_rendezvous_in(struct sched_item *prev, static void sched_slave(void) { - struct vcpu *vprev = current; + struct vcpu *v, *vprev = current; struct sched_item *prev = vprev->sched_item, *next; s_time_t now; spinlock_t *lock; + bool do_softirq = false; int cpu = smp_processor_id(); ASSERT_NOT_IN_ATOMIC(); @@ -1882,9 +1974,29 @@ static void sched_slave(void) now = NOW(); + v = item2vcpu_cpu(prev, cpu); + if ( v && v->force_context_switch ) + { + v = sched_force_context_switch(vprev, v, cpu, now); + + if ( v ) + { + pcpu_schedule_unlock_irq(lock, cpu); + + sched_context_switch(vprev, v, false, now); + } + + do_softirq = true; + } + if ( !prev->rendezvous_in_cnt ) { pcpu_schedule_unlock_irq(lock, cpu); + + /* Check for failed forced context switch. */ + if ( do_softirq ) + raise_softirq(SCHEDULE_SOFTIRQ); + return; } diff --git a/xen/include/xen/sched-if.h b/xen/include/xen/sched-if.h index 8981d41629..f16d81ab4a 100644 --- a/xen/include/xen/sched-if.h +++ b/xen/include/xen/sched-if.h @@ -75,6 +75,11 @@ static inline bool item_runnable(const struct sched_item *item) return false; } +static inline int vcpu_runstate_blocked(struct vcpu *v) +{ + return (v->pause_flags & VPF_blocked) ? RUNSTATE_blocked : RUNSTATE_offline; +} + static inline bool item_runnable_state(const struct sched_item *item) { struct vcpu *v; @@ -84,9 +89,7 @@ static inline bool item_runnable_state(const struct sched_item *item) { runnable = vcpu_runnable(v); - v->new_state = runnable ? RUNSTATE_running - : (v->pause_flags & VPF_blocked) - ? RUNSTATE_blocked : RUNSTATE_offline; + v->new_state = runnable ? RUNSTATE_running : vcpu_runstate_blocked(v); if ( runnable ) ret = true; diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h index b6a2fe28cc..5629602de5 100644 --- a/xen/include/xen/sched.h +++ b/xen/include/xen/sched.h @@ -186,6 +186,8 @@ struct vcpu bool is_running; /* VCPU should wake fast (do not deep sleep the CPU). */ bool is_urgent; + /* VCPU must context_switch without scheduling item. */ + bool force_context_switch; #ifdef VCPU_TRAP_LAST #define VCPU_TRAP_NONE 0 -- 2.16.4 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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