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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] xen: credit2: make tickling more deterministic
commit 069cf39fb1715bc8f43dc3f9b332fe6b6b778611
Author: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
AuthorDate: Fri Sep 30 04:53:39 2016 +0200
Commit: George Dunlap <george.dunlap@xxxxxxxxxx>
CommitDate: Fri Sep 30 14:46:36 2016 +0100
xen: credit2: make tickling more deterministic
Right now, the following scenario can occurr:
- upon vcpu v wakeup, v itself is put in the runqueue,
and pcpu X is tickled;
- pcpu Y schedules (for whatever reason), sees v in
the runqueue and picks it up.
This may seem ok (or even a good thing), but it's not.
In fact, if runq_tickle() decided X is where v should
run, it did it for a reason (load distribution, SMT
support, cache hotness, affinity, etc), and we really
should try as hard as possible to stick to that.
Of course, we can't be too strict, or we risk leaving
vcpus in the runqueue while there is available CPU
capacity. So, we only leave v in runqueue --for X to
pick it up-- if we see that X has been tickled and
has not scheduled yet, i.e., it will have a real chance
of actually select and schedule v.
If that is not the case, we schedule it on Y (or, at
least, we consider that), as running somewhere non-ideal
is better than not running at all.
The commit also adds performance counters for each of
the possible situations.
Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>
---
xen/common/sched_credit2.c | 37 ++++++++++++++++++++++++++++++++++++-
xen/include/xen/perfc_defn.h | 3 +++
2 files changed, 39 insertions(+), 1 deletion(-)
diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 5c7d0dc..3986441 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -54,6 +54,7 @@
#define TRC_CSCHED2_LOAD_CHECK TRC_SCHED_CLASS_EVT(CSCHED2, 16)
#define TRC_CSCHED2_LOAD_BALANCE TRC_SCHED_CLASS_EVT(CSCHED2, 17)
#define TRC_CSCHED2_PICKED_CPU TRC_SCHED_CLASS_EVT(CSCHED2, 19)
+#define TRC_CSCHED2_RUNQ_CANDIDATE TRC_SCHED_CLASS_EVT(CSCHED2, 20)
/*
* WARNING: This is still in an experimental phase. Status and work can be
found at the
@@ -398,6 +399,7 @@ struct csched2_vcpu {
int credit;
s_time_t start_time; /* When we were scheduled (used for credit) */
unsigned flags; /* 16 bits doesn't seem to play well with clear_bit()
*/
+ int tickled_cpu; /* cpu tickled for picking us up (-1 if none) */
/* Individual contribution to load */
s_time_t load_last_update; /* Last time average was updated */
@@ -1049,6 +1051,10 @@ runq_tickle(const struct scheduler *ops, struct
csched2_vcpu *new, s_time_t now)
__cpumask_set_cpu(ipid, &rqd->tickled);
smt_idle_mask_clear(ipid, &rqd->smt_idle);
cpu_raise_softirq(ipid, SCHEDULE_SOFTIRQ);
+
+ if ( unlikely(new->tickled_cpu != -1) )
+ SCHED_STAT_CRANK(tickled_cpu_overwritten);
+ new->tickled_cpu = ipid;
}
/*
@@ -1276,6 +1282,7 @@ csched2_alloc_vdata(const struct scheduler *ops, struct
vcpu *vc, void *dd)
svc->credit = CSCHED2_IDLE_CREDIT;
svc->weight = 0;
}
+ svc->tickled_cpu = -1;
SCHED_STAT_CRANK(vcpu_alloc);
@@ -2268,6 +2275,17 @@ runq_candidate(struct csched2_runqueue_data *rqd,
if ( !cpumask_test_cpu(cpu, svc->vcpu->cpu_hard_affinity) )
continue;
+ /*
+ * If a vcpu is meant to be picked up by another processor, and such
+ * processor has not scheduled yet, leave it in the runqueue for him.
+ */
+ if ( svc->tickled_cpu != -1 && svc->tickled_cpu != cpu &&
+ cpumask_test_cpu(svc->tickled_cpu, &rqd->tickled) )
+ {
+ SCHED_STAT_CRANK(deferred_to_tickled_cpu);
+ continue;
+ }
+
/* If this is on a different processor, don't pull it unless
* its credit is at least CSCHED2_MIGRATE_RESIST higher. */
if ( svc->vcpu->processor != cpu
@@ -2284,9 +2302,25 @@ runq_candidate(struct csched2_runqueue_data *rqd,
/* In any case, if we got this far, break. */
break;
+ }
+ if ( unlikely(tb_init_done) )
+ {
+ struct {
+ unsigned vcpu:16, dom:16;
+ unsigned tickled_cpu;
+ } d;
+ d.dom = snext->vcpu->domain->domain_id;
+ d.vcpu = snext->vcpu->vcpu_id;
+ d.tickled_cpu = snext->tickled_cpu;
+ __trace_var(TRC_CSCHED2_RUNQ_CANDIDATE, 1,
+ sizeof(d),
+ (unsigned char *)&d);
}
+ if ( unlikely(snext->tickled_cpu != -1 && snext->tickled_cpu != cpu) )
+ SCHED_STAT_CRANK(tickled_cpu_overridden);
+
return snext;
}
@@ -2351,7 +2385,7 @@ csched2_schedule(
snext = CSCHED2_VCPU(idle_vcpu[cpu]);
}
else
- snext=runq_candidate(rqd, scurr, cpu, now);
+ snext = runq_candidate(rqd, scurr, cpu, now);
/* If switching from a non-idle runnable vcpu, put it
* back on the runqueue. */
@@ -2390,6 +2424,7 @@ csched2_schedule(
}
snext->start_time = now;
+ snext->tickled_cpu = -1;
/* Safe because lock for old processor is held */
if ( snext->vcpu->processor != cpu )
diff --git a/xen/include/xen/perfc_defn.h b/xen/include/xen/perfc_defn.h
index a336c71..4a835b8 100644
--- a/xen/include/xen/perfc_defn.h
+++ b/xen/include/xen/perfc_defn.h
@@ -66,6 +66,9 @@ PERFCOUNTER(runtime_max_timer, "csched2:
runtime_max_timer")
PERFCOUNTER(migrated, "csched2: migrated")
PERFCOUNTER(migrate_resisted, "csched2: migrate_resisted")
PERFCOUNTER(credit_reset, "csched2: credit_reset")
+PERFCOUNTER(deferred_to_tickled_cpu,"csched2: deferred_to_tickled_cpu")
+PERFCOUNTER(tickled_cpu_overwritten,"csched2: tickled_cpu_overwritten")
+PERFCOUNTER(tickled_cpu_overridden, "csched2: tickled_cpu_overridden")
PERFCOUNTER(need_flush_tlb_flush, "PG_need_flush tlb flushes")
--
generated by git-patchbot for /home/xen/git/xen.git#master
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