The null scheduler does not really use hard-affinity for scheduling, it uses it for 'placement', i.e., for deciding to what pCPU to statically assign a vCPU.
Let's use soft-affinity in the same way, of course with the difference that, if there's no free pCPU within the vCPU's soft-affinity, we go checking the hard-affinity, instead of putting the vCPU in the waitqueue. This does has no impact on the scheduling overhead, because soft-affinity is only considered in cold-path (like when a vCPU joins the scheduler for the first time, or is manually moved between pCPUs by the user). Signed-off-by: Dario Faggioli <dario.faggi...@citrix.com> --- Cc: George Dunlap <george.dun...@eu.citrix.com> --- xen/common/sched_null.c | 110 +++++++++++++++++++++++++++++++++-------------- 1 file changed, 77 insertions(+), 33 deletions(-) diff --git a/xen/common/sched_null.c b/xen/common/sched_null.c index 610a150..19c7f0f 100644 --- a/xen/common/sched_null.c +++ b/xen/common/sched_null.c @@ -115,9 +115,11 @@ static inline struct null_dom *null_dom(const struct domain *d) return d->sched_priv; } -static inline bool vcpu_check_affinity(struct vcpu *v, unsigned int cpu) +static inline bool vcpu_check_affinity(struct vcpu *v, unsigned int cpu, + unsigned int balance_step) { - cpumask_and(cpumask_scratch_cpu(cpu), v->cpu_hard_affinity, + affinity_balance_cpumask(v, balance_step, cpumask_scratch_cpu(cpu)); + cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu), cpupool_domain_cpumask(v->domain)); return cpumask_test_cpu(cpu, cpumask_scratch_cpu(cpu)); @@ -279,31 +281,40 @@ static void null_dom_destroy(const struct scheduler *ops, struct domain *d) */ static unsigned int pick_cpu(struct null_private *prv, struct vcpu *v) { + unsigned int bs; unsigned int cpu = v->processor, new_cpu; cpumask_t *cpus = cpupool_domain_cpumask(v->domain); ASSERT(spin_is_locked(per_cpu(schedule_data, cpu).schedule_lock)); - cpumask_and(cpumask_scratch_cpu(cpu), v->cpu_hard_affinity, cpus); + for_each_affinity_balance_step( bs ) + { + if ( bs == BALANCE_SOFT_AFFINITY && + !has_soft_affinity(v, v->cpu_hard_affinity) ) + continue; - /* - * If our processor is free, or we are assigned to it, and it is also - * still valid and part of our affinity, just go for it. - * (Note that we may call vcpu_check_affinity(), but we deliberately - * don't, so we get to keep in the scratch cpumask what we have just - * put in it.) - */ - if ( likely((per_cpu(npc, cpu).vcpu == NULL || per_cpu(npc, cpu).vcpu == v) - && cpumask_test_cpu(cpu, cpumask_scratch_cpu(cpu))) ) - return cpu; + affinity_balance_cpumask(v, bs, cpumask_scratch_cpu(cpu)); + cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu), cpus); - /* If not, just go for a free pCPU, within our affinity, if any */ - cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu), - &prv->cpus_free); - new_cpu = cpumask_first(cpumask_scratch_cpu(cpu)); + /* + * If our processor is free, or we are assigned to it, and it is also + * still valid and part of our affinity, just go for it. + * (Note that we may call vcpu_check_affinity(), but we deliberately + * don't, so we get to keep in the scratch cpumask what we have just + * put in it.) + */ + if ( likely((per_cpu(npc, cpu).vcpu == NULL || per_cpu(npc, cpu).vcpu == v) + && cpumask_test_cpu(cpu, cpumask_scratch_cpu(cpu))) ) + return cpu; - if ( likely(new_cpu != nr_cpu_ids) ) - return new_cpu; + /* If not, just go for a free pCPU, within our affinity, if any */ + cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu), + &prv->cpus_free); + new_cpu = cpumask_first(cpumask_scratch_cpu(cpu)); + + if ( likely(new_cpu != nr_cpu_ids) ) + return new_cpu; + } /* * If we didn't find any free pCPU, just pick any valid pcpu, even if @@ -430,6 +441,7 @@ static void null_vcpu_insert(const struct scheduler *ops, struct vcpu *v) static void _vcpu_remove(struct null_private *prv, struct vcpu *v) { + unsigned int bs; unsigned int cpu = v->processor; struct null_vcpu *wvc; @@ -441,19 +453,27 @@ static void _vcpu_remove(struct null_private *prv, struct vcpu *v) /* * If v is assigned to a pCPU, let's see if there is someone waiting, - * suitable to be assigned to it. + * suitable to be assigned to it (prioritizing vcpus that have + * soft-affinity with cpu). */ - list_for_each_entry( wvc, &prv->waitq, waitq_elem ) + for_each_affinity_balance_step( bs ) { - if ( vcpu_check_affinity(wvc->vcpu, cpu) ) + list_for_each_entry( wvc, &prv->waitq, waitq_elem ) { - list_del_init(&wvc->waitq_elem); - vcpu_assign(prv, wvc->vcpu, cpu); - cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ); - break; + if ( bs == BALANCE_SOFT_AFFINITY && + !has_soft_affinity(wvc->vcpu, wvc->vcpu->cpu_hard_affinity) ) + continue; + + if ( vcpu_check_affinity(wvc->vcpu, cpu, bs) ) + { + list_del_init(&wvc->waitq_elem); + vcpu_assign(prv, wvc->vcpu, cpu); + cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ); + spin_unlock(&prv->waitq_lock); + return; + } } } - spin_unlock(&prv->waitq_lock); } @@ -570,7 +590,8 @@ static void null_vcpu_migrate(const struct scheduler *ops, struct vcpu *v, * * In latter, all we can do is to park v in the waitqueue. */ - if ( per_cpu(npc, new_cpu).vcpu == NULL && vcpu_check_affinity(v, new_cpu) ) + if ( per_cpu(npc, new_cpu).vcpu == NULL && + vcpu_check_affinity(v, new_cpu, BALANCE_HARD_AFFINITY) ) { /* v might have been in the waitqueue, so remove it */ spin_lock(&prv->waitq_lock); @@ -633,6 +654,7 @@ static struct task_slice null_schedule(const struct scheduler *ops, s_time_t now, bool_t tasklet_work_scheduled) { + unsigned int bs; const unsigned int cpu = smp_processor_id(); struct null_private *prv = null_priv(ops); struct null_vcpu *wvc; @@ -656,13 +678,35 @@ static struct task_slice null_schedule(const struct scheduler *ops, if ( unlikely(ret.task == NULL) ) { spin_lock(&prv->waitq_lock); - wvc = list_first_entry_or_null(&prv->waitq, struct null_vcpu, waitq_elem); - if ( wvc && vcpu_check_affinity(wvc->vcpu, cpu) ) + + if ( list_empty(&prv->waitq) ) + goto unlock; + + /* + * We scan the waitqueue twice, for prioritizing vcpus that have + * soft-affinity with cpu. This may look like something expensive to + * do here in null_schedule(), but it's actually fine, beceuse we do + * it only in cases where a pcpu has no vcpu associated (e.g., as + * said above, the cpu has just joined a cpupool). + */ + for_each_affinity_balance_step( bs ) { - vcpu_assign(prv, wvc->vcpu, cpu); - list_del_init(&wvc->waitq_elem); - ret.task = wvc->vcpu; + list_for_each_entry( wvc, &prv->waitq, waitq_elem ) + { + if ( bs == BALANCE_SOFT_AFFINITY && + !has_soft_affinity(wvc->vcpu, wvc->vcpu->cpu_hard_affinity) ) + continue; + + if ( vcpu_check_affinity(wvc->vcpu, cpu, bs) ) + { + vcpu_assign(prv, wvc->vcpu, cpu); + list_del_init(&wvc->waitq_elem); + ret.task = wvc->vcpu; + goto unlock; + } + } } + unlock: spin_unlock(&prv->waitq_lock); } _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel