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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 4/7] xen: credit2: soft-affinity awareness in csched2_cpu_pick()
We want to find the runqueue with the least average load,
and to do that, we scan through all the runqueues.
It is, therefore, enough that, during such scan:
- we identify the runqueue with the least load, among
the ones that have pcpus that are part of the soft
affinity of the vcpu we're calling pick on;
- we identify the same, but for hard affinity.
At this point, we can decide whether to go for the
runqueue with the least load among the ones with some
soft-affinity, or overall.
Therefore, at the price of some code reshuffling, we
can avoid the loop.
(Also, kill a spurious ';' in the definition of MAX_LOAD.)
Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Signed-off-by: Justin T. Weaver <jtweaver@xxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
Cc: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
---
xen/common/sched_credit2.c | 117 ++++++++++++++++++++++++++++++++++++--------
1 file changed, 97 insertions(+), 20 deletions(-)
diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 54f6e21..fb97ff7 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -1725,14 +1725,16 @@ csched2_context_saved(const struct scheduler *ops,
struct vcpu *vc)
vcpu_schedule_unlock_irq(lock, vc);
}
-#define MAX_LOAD (STIME_MAX);
+#define MAX_LOAD (STIME_MAX)
static int
csched2_cpu_pick(const struct scheduler *ops, struct vcpu *vc)
{
struct csched2_private *prv = csched2_priv(ops);
- int i, min_rqi = -1, new_cpu, cpu = vc->processor;
+ int i, min_rqi = -1, min_s_rqi = -1;
+ unsigned int new_cpu, cpu = vc->processor;
struct csched2_vcpu *svc = csched2_vcpu(vc);
- s_time_t min_avgload = MAX_LOAD;
+ s_time_t min_avgload = MAX_LOAD, min_s_avgload = MAX_LOAD;
+ bool has_soft;
ASSERT(!cpumask_empty(&prv->active_queues));
@@ -1781,17 +1783,35 @@ csched2_cpu_pick(const struct scheduler *ops, struct
vcpu *vc)
else if ( cpumask_intersects(cpumask_scratch_cpu(cpu),
&svc->migrate_rqd->active) )
{
+ /*
+ * If we've been asked to move to migrate_rqd, we should just do
+ * that, which we actually do by returning one cpu from that runq.
+ * There is no need to take care of soft affinity, as that will
+ * happen in runq_tickle().
+ */
cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
&svc->migrate_rqd->active);
new_cpu = cpumask_cycle(svc->migrate_rqd->pick_bias,
cpumask_scratch_cpu(cpu));
+
svc->migrate_rqd->pick_bias = new_cpu;
goto out_up;
}
/* Fall-through to normal cpu pick */
}
- /* Find the runqueue with the lowest average load. */
+ /*
+ * What we want is:
+ * - if we have soft affinity, the runqueue with the lowest average
+ * load, among the ones that contain cpus in our soft affinity; this
+ * represents the best runq on which we would want to run.
+ * - the runqueue with the lowest average load among the ones that
+ * contains cpus in our hard affinity; this represent the best runq
+ * on which we can run.
+ *
+ * Find both runqueues in one pass.
+ */
+ has_soft = has_soft_affinity(vc, vc->cpu_hard_affinity);
for_each_cpu(i, &prv->active_queues)
{
struct csched2_runqueue_data *rqd;
@@ -1800,31 +1820,51 @@ csched2_cpu_pick(const struct scheduler *ops, struct
vcpu *vc)
rqd = prv->rqd + i;
/*
- * If checking a different runqueue, grab the lock, check hard
- * affinity, read the avg, and then release the lock.
+ * If none of the cpus of this runqueue is in svc's hard-affinity,
+ * skip the runqueue.
+ *
+ * Note that, in case svc's hard-affinity has changed, this is the
+ * first time when we see such change, so it is indeed possible
+ * that we end up skipping svc's current runqueue.
+ */
+ if ( !cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active) )
+ continue;
+
+ /*
+ * If checking a different runqueue, grab the lock, read the avg,
+ * and then release the lock.
*
* If on our own runqueue, don't grab or release the lock;
* but subtract our own load from the runqueue load to simulate
* impartiality.
- *
- * Note that, if svc's hard affinity has changed, this is the
- * first time when we see such change, so it is indeed possible
- * that none of the cpus in svc's current runqueue is in our
- * (new) hard affinity!
*/
if ( rqd == svc->rqd )
{
- if ( cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active) )
- rqd_avgload = max_t(s_time_t, rqd->b_avgload - svc->avgload,
0);
+ rqd_avgload = max_t(s_time_t, rqd->b_avgload - svc->avgload, 0);
}
else if ( spin_trylock(&rqd->lock) )
{
- if ( cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active) )
- rqd_avgload = rqd->b_avgload;
-
+ rqd_avgload = rqd->b_avgload;
spin_unlock(&rqd->lock);
}
+ /*
+ * if svc has a soft-affinity, and some cpus of rqd are part of it,
+ * see if we need to update the "soft-affinity minimum".
+ */
+ if ( has_soft &&
+ rqd_avgload < min_s_avgload )
+ {
+ cpumask_t mask;
+
+ cpumask_and(&mask, cpumask_scratch_cpu(cpu), &rqd->active);
+ if ( cpumask_intersects(&mask, svc->vcpu->cpu_soft_affinity) )
+ {
+ min_s_avgload = rqd_avgload;
+ min_s_rqi = i;
+ }
+ }
+ /* In any case, keep the "hard-affinity minimum" updated too. */
if ( rqd_avgload < min_avgload )
{
min_avgload = rqd_avgload;
@@ -1832,17 +1872,54 @@ csched2_cpu_pick(const struct scheduler *ops, struct
vcpu *vc)
}
}
- /* We didn't find anyone (most likely because of spinlock contention). */
- if ( min_rqi == -1 )
+ if ( has_soft && min_s_rqi != -1 )
+ {
+ /*
+ * We have soft affinity, and we have a candidate runq, so go for it.
+ *
+ * Note that, to obtain the soft-affinity mask, we "just" put what we
+ * have in cpumask_scratch in && with vc->cpu_soft_affinity. This is
+ * ok because:
+ * - we know that vc->cpu_hard_affinity and vc->cpu_soft_affinity have
+ * a non-empty intersection (because has_soft is true);
+ * - we have vc->cpu_hard_affinity & cpupool_domain_cpumask() already
+ * in cpumask_scratch, we do save a lot doing like this.
+ *
+ * It's kind of like open coding affinity_balance_cpumask() but, in
+ * this specific case, calling that would mean a lot of (unnecessary)
+ * cpumask operations.
+ */
+ cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
+ vc->cpu_soft_affinity);
+ cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
+ &prv->rqd[min_s_rqi].active);
+ }
+ else if ( min_rqi != -1 )
{
+ /*
+ * Either we don't have soft-affinity, or we do, but we did not find
+ * any suitable runq. But we did find one when considering hard
+ * affinity, so go for it.
+ *
+ * cpumask_scratch already has vc->cpu_hard_affinity &
+ * cpupool_domain_cpumask() in it, so it's enough that we filter
+ * with the cpus of the runq.
+ */
+ cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
+ &prv->rqd[min_rqi].active);
+ }
+ else
+ {
+ /*
+ * We didn't find anyone at all (most likely because of spinlock
+ * contention).
+ */
new_cpu = get_fallback_cpu(svc);
min_rqi = c2r(ops, new_cpu);
min_avgload = prv->rqd[min_rqi].b_avgload;
goto out_up;
}
- cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
- &prv->rqd[min_rqi].active);
new_cpu = cpumask_cycle(prv->rqd[min_rqi].pick_bias,
cpumask_scratch_cpu(cpu));
prv->rqd[min_rqi].pick_bias = new_cpu;
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