Resist moving a vcpu from one L2 to another unless its credit
is past a certain amount.
Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
diff -r c48e8e6b9a69 -r 91c3f237d40d xen/common/sched_credit2.c
--- a/xen/common/sched_credit2.c Thu Dec 09 17:50:54 2010 +0000
+++ b/xen/common/sched_credit2.c Thu Dec 09 17:50:54 2010 +0000
@@ -116,6 +116,11 @@
/* Carryover: How much "extra" credit may be carried over after
* a reset. */
#define CSCHED_CARRYOVER_MAX CSCHED_MIN_TIMER
+/* Stickiness: Cross-L2 migration resistance. Should be less than
+ * MIN_TIMER. */
+#define CSCHED_MIGRATE_RESIST ((opt_migrate_resist)*MICROSECS(1))
+/* How much to "compensate" a vcpu for L2 migration */
+#define CSCHED_MIGRATE_COMPENSATION MICROSECS(50)
/* Reset: Value below which credit will be reset. */
#define CSCHED_CREDIT_RESET 0
/* Max timer: Maximum time a guest can be run for. */
@@ -149,6 +154,9 @@
#define CSFLAG_delayed_runq_add (1<<__CSFLAG_delayed_runq_add)
+int opt_migrate_resist=500;
+integer_param("sched_credit2_migrate_resist", opt_migrate_resist);
+
/*
* Useful macros
*/
@@ -406,8 +414,9 @@
}
}
- /* At this point, if ipid is non-zero, see if the lowest is lower than new
*/
- if ( ipid == -1 || lowest > new->credit )
+ /* Only switch to another processor if the credit difference is greater
+ * than the migrate resistance */
+ if ( ipid == -1 || lowest + CSCHED_MIGRATE_RESIST > new->credit )
goto no_tickle;
tickle:
@@ -940,6 +949,46 @@
void __dump_execstate(void *unused);
/*
+ * Find a candidate.
+ */
+static struct csched_vcpu *
+runq_candidate(struct csched_runqueue_data *rqd,
+ struct csched_vcpu *scurr,
+ int cpu, s_time_t now)
+{
+ struct list_head *iter;
+ struct csched_vcpu *snext = NULL;
+
+ /* Default to current if runnable, idle otherwise */
+ if ( vcpu_runnable(scurr->vcpu) )
+ snext = scurr;
+ else
+ snext = CSCHED_VCPU(idle_vcpu[cpu]);
+
+ list_for_each( iter, &rqd->runq )
+ {
+ struct csched_vcpu * svc = list_entry(iter, struct csched_vcpu,
runq_elem);
+
+ /* If this is on a different processor, don't pull it unless
+ * its credit is at least CSCHED_MIGRATE_RESIST higher. */
+ if ( svc->vcpu->processor != cpu
+ && snext->credit + CSCHED_MIGRATE_RESIST > svc->credit )
+ continue;
+
+ /* If the next one on the list has more credit than current
+ * (or idle, if current is not runnable), choose it. */
+ if ( svc->credit > snext->credit )
+ snext = svc;
+
+ /* In any case, if we got this far, break. */
+ break;
+
+ }
+
+ return snext;
+}
+
+/*
* This function is in the critical path. It is designed to be simple and
* fast for the common case.
*/
@@ -949,7 +998,6 @@
{
const int cpu = smp_processor_id();
struct csched_runqueue_data *rqd = RQD(ops, cpu);
- struct list_head * const runq = &rqd->runq;
struct csched_vcpu * const scurr = CSCHED_VCPU(current);
struct csched_vcpu *snext = NULL;
struct task_slice ret;
@@ -983,80 +1031,74 @@
* for this processor, and mark the current for delayed runqueue
* add.
*
- * If the current vcpu is runnable, and the next guy on the queue
- * has higher credit, we want to mark current for delayed runqueue
- * add, and remove the next guy from the queue.
+ * If the current vcpu is runnable, and there's another runnable
+ * candidate, we want to mark current for delayed runqueue add,
+ * and remove the next guy from the queue.
*
* If the current vcpu is not runnable, we want to chose the idle
* vcpu for this processor.
*/
- if ( list_empty(runq) || tasklet_work_scheduled )
+ if ( tasklet_work_scheduled )
+ {
+ trace_var(TRC_CSCHED2_SCHED_TASKLET, 0, 0, NULL);
snext = CSCHED_VCPU(idle_vcpu[cpu]);
+ }
else
- snext = __runq_elem(runq->next);
+ snext=runq_candidate(rqd, scurr, cpu, now);
- if ( tasklet_work_scheduled )
- trace_var(TRC_CSCHED2_SCHED_TASKLET, 0, 0, NULL);
-
- if ( !is_idle_vcpu(current) && vcpu_runnable(current) )
- {
- /* If the current vcpu is runnable, and has higher credit
- * than the next on the runqueue, and isn't being preempted
- * by a tasklet, run him again.
- * Otherwise, set him for delayed runq add. */
-
- if ( !tasklet_work_scheduled && scurr->credit > snext->credit)
- snext = scurr;
- else
- set_bit(__CSFLAG_delayed_runq_add, &scurr->flags);
-
- }
-
- if ( snext != scurr && !is_idle_vcpu(snext->vcpu) )
- {
- __runq_remove(snext);
- if ( snext->vcpu->is_running )
- {
- printk("p%d: snext d%dv%d running on p%d! scurr d%dv%d\n",
- cpu,
- snext->vcpu->domain->domain_id, snext->vcpu->vcpu_id,
- snext->vcpu->processor,
- scurr->vcpu->domain->domain_id,
- scurr->vcpu->vcpu_id);
- BUG();
- }
- set_bit(__CSFLAG_scheduled, &snext->flags);
- }
-
- if ( !is_idle_vcpu(snext->vcpu) && snext->credit <= CSCHED_CREDIT_RESET )
- reset_credit(ops, cpu, now);
-
- /*
- * Update idlers mask if necessary. When we're idling, other CPUs
- * will tickle us when they get extra work.
- */
- if ( is_idle_vcpu(snext->vcpu) )
- {
- if ( !cpu_isset(cpu, rqd->idle) )
- cpu_set(cpu, rqd->idle);
- }
- else if ( cpu_isset(cpu, rqd->idle) )
- {
- cpu_clear(cpu, rqd->idle);
- }
+ /* If switching from a non-idle runnable vcpu, put it
+ * back on the runqueue. */
+ if ( snext != scurr
+ && !is_idle_vcpu(scurr->vcpu)
+ && vcpu_runnable(current) )
+ set_bit(__CSFLAG_delayed_runq_add, &scurr->flags);
ret.migrated = 0;
+ /* Accounting for non-idle tasks */
if ( !is_idle_vcpu(snext->vcpu) )
{
+ /* If switching, remove this from the runqueue and mark it scheduled */
+ if ( snext != scurr )
+ {
+ __runq_remove(snext);
+ if ( snext->vcpu->is_running )
+ {
+ printk("p%d: snext d%dv%d running on p%d! scurr d%dv%d\n",
+ cpu,
+ snext->vcpu->domain->domain_id, snext->vcpu->vcpu_id,
+ snext->vcpu->processor,
+ scurr->vcpu->domain->domain_id,
+ scurr->vcpu->vcpu_id);
+ BUG();
+ }
+ set_bit(__CSFLAG_scheduled, &snext->flags);
+ }
+
+ /* Check for the reset condition */
+ if ( snext->credit <= CSCHED_CREDIT_RESET )
+ reset_credit(ops, cpu, now);
+
+ /* Clear the idle mask if necessary */
+ if ( cpu_isset(cpu, rqd->idle) )
+ cpu_clear(cpu, rqd->idle);
+
snext->start_time = now;
+
/* Safe because lock for old processor is held */
if ( snext->vcpu->processor != cpu )
{
+ snext->credit += CSCHED_MIGRATE_COMPENSATION;
snext->vcpu->processor = cpu;
ret.migrated = 1;
}
}
+ else
+ {
+ /* Update the idle mask if necessary */
+ if ( !cpu_isset(cpu, rqd->idle) )
+ cpu_set(cpu, rqd->idle);
+ }
/*
* Return task to run next...
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