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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen stable-4.12] credit2: fix credit reset happening too few times
commit c1a1c4e8fb54038aee36305531426da4e3ad3872
Author: Dario Faggioli <dfaggioli@xxxxxxxx>
AuthorDate: Thu Apr 9 09:36:51 2020 +0200
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Apr 9 09:36:51 2020 +0200
credit2: fix credit reset happening too few times
There is a bug in commit 5e4b4199667b9 ("xen: credit2: only reset
credit on reset condition"). In fact, the aim of that commit was to
make sure that we do not perform too many credit reset operations
(which are not super cheap, and in an hot-path). But the check used
to determine whether a reset is necessary was the wrong one.
In fact, knowing just that some vCPUs have been skipped, while
traversing the runqueue (in runq_candidate()), is not enough. We
need to check explicitly whether the first vCPU in the runqueue
has a negative amount of credit.
Since a trace record is changed, this patch updates xentrace format file
and xenalyze as well
This should be backported.
Signed-off-by: Dario Faggioli <dfaggioli@xxxxxxxx>
Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>
master commit: dae7b62e976b28af9c8efa150618c25501bf1650
master date: 2020-04-03 10:46:53 +0200
---
tools/xentrace/formats | 2 +-
tools/xentrace/xenalyze.c | 8 +++-----
xen/common/sched_credit2.c | 28 ++++++++++++----------------
3 files changed, 16 insertions(+), 22 deletions(-)
diff --git a/tools/xentrace/formats b/tools/xentrace/formats
index 8f126f65f1..deac4d8598 100644
--- a/tools/xentrace/formats
+++ b/tools/xentrace/formats
@@ -67,7 +67,7 @@
0x00022210 CPU%(cpu)d %(tsc)d (+%(reltsc)8d) csched2:load_check [
lrq_id[16]:orq_id[16] = 0x%(1)08x, delta = %(2)d ]
0x00022211 CPU%(cpu)d %(tsc)d (+%(reltsc)8d) csched2:load_balance [
l_bavgload = 0x%(2)08x%(1)08x, o_bavgload = 0x%(4)08x%(3)08x,
lrq_id[16]:orq_id[16] = 0x%(5)08x ]
0x00022212 CPU%(cpu)d %(tsc)d (+%(reltsc)8d) csched2:pick_cpu [
b_avgload = 0x%(2)08x%(1)08x, dom:vcpu = 0x%(3)08x, rq_id[16]:new_cpu[16] =
%(4)d ]
-0x00022213 CPU%(cpu)d %(tsc)d (+%(reltsc)8d) csched2:runq_candidate [
dom:vcpu = 0x%(1)08x, credit = %(4)d, skipped_vcpus = %(3)d, tickled_cpu =
%(2)d ]
+0x00022213 CPU%(cpu)d %(tsc)d (+%(reltsc)8d) csched2:runq_candidate [
dom:vcpu = 0x%(1)08x, credit = %(3)d, tickled_cpu = %(2)d ]
0x00022214 CPU%(cpu)d %(tsc)d (+%(reltsc)8d) csched2:schedule [
rq:cpu = 0x%(1)08x, tasklet[8]:idle[8]:smt_idle[8]:tickled[8] = %(2)08x ]
0x00022215 CPU%(cpu)d %(tsc)d (+%(reltsc)8d) csched2:ratelimit [
dom:vcpu = 0x%(1)08x, runtime = %(2)d ]
0x00022216 CPU%(cpu)d %(tsc)d (+%(reltsc)8d) csched2:runq_cand_chk [
dom:vcpu = 0x%(1)08x ]
diff --git a/tools/xentrace/xenalyze.c b/tools/xentrace/xenalyze.c
index d3c8368e9d..b7f4e2bea8 100644
--- a/tools/xentrace/xenalyze.c
+++ b/tools/xentrace/xenalyze.c
@@ -7855,14 +7855,12 @@ void sched_process(struct pcpu_info *p)
if (opt.dump_all) {
struct {
unsigned vcpuid:16, domid:16;
- unsigned tickled_cpu, skipped;
+ unsigned tickled_cpu;
int credit;
} *r = (typeof(r))ri->d;
- printf(" %s csched2:runq_candidate d%uv%u, credit = %d, "
- "%u vcpus skipped, ",
- ri->dump_header, r->domid, r->vcpuid,
- r->credit, r->skipped);
+ printf(" %s csched2:runq_candidate d%uv%u, credit = %d, ",
+ ri->dump_header, r->domid, r->vcpuid, r->credit);
if (r->tickled_cpu == (unsigned)-1)
printf("no cpu was tickled\n");
else
diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 4e7f0aa29e..d6ebd126de 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -3260,16 +3260,13 @@ csched2_runtime(const struct scheduler *ops, int cpu,
static struct csched2_vcpu *
runq_candidate(struct csched2_runqueue_data *rqd,
struct csched2_vcpu *scurr,
- int cpu, s_time_t now,
- unsigned int *skipped)
+ int cpu, s_time_t now)
{
struct list_head *iter, *temp;
struct csched2_vcpu *snext = NULL;
struct csched2_private *prv = csched2_priv(per_cpu(scheduler, cpu));
bool yield = false, soft_aff_preempt = false;
- *skipped = 0;
-
if ( unlikely(is_idle_vcpu(scurr->vcpu)) )
{
snext = scurr;
@@ -3366,10 +3363,7 @@ runq_candidate(struct csched2_runqueue_data *rqd,
/* Only consider vcpus that are allowed to run on this processor. */
if ( !cpumask_test_cpu(cpu, svc->vcpu->cpu_hard_affinity) )
- {
- (*skipped)++;
continue;
- }
/*
* If a vcpu is meant to be picked up by another processor, and such
@@ -3378,7 +3372,6 @@ runq_candidate(struct csched2_runqueue_data *rqd,
if ( svc->tickled_cpu != -1 && svc->tickled_cpu != cpu &&
cpumask_test_cpu(svc->tickled_cpu, &rqd->tickled) )
{
- (*skipped)++;
SCHED_STAT_CRANK(deferred_to_tickled_cpu);
continue;
}
@@ -3390,7 +3383,6 @@ runq_candidate(struct csched2_runqueue_data *rqd,
if ( svc->vcpu->processor != cpu
&& snext->credit + CSCHED2_MIGRATE_RESIST > svc->credit )
{
- (*skipped)++;
SCHED_STAT_CRANK(migrate_resisted);
continue;
}
@@ -3413,14 +3405,13 @@ runq_candidate(struct csched2_runqueue_data *rqd,
{
struct {
unsigned vcpu:16, dom:16;
- unsigned tickled_cpu, skipped;
+ unsigned tickled_cpu;
int credit;
} d;
d.dom = snext->vcpu->domain->domain_id;
d.vcpu = snext->vcpu->vcpu_id;
d.credit = snext->credit;
d.tickled_cpu = snext->tickled_cpu;
- d.skipped = *skipped;
__trace_var(TRC_CSCHED2_RUNQ_CANDIDATE, 1,
sizeof(d),
(unsigned char *)&d);
@@ -3451,7 +3442,6 @@ csched2_schedule(
struct csched2_runqueue_data *rqd;
struct csched2_vcpu * const scurr = csched2_vcpu(current);
struct csched2_vcpu *snext = NULL;
- unsigned int skipped_vcpus = 0;
struct task_slice ret;
bool tickled;
@@ -3529,7 +3519,7 @@ csched2_schedule(
snext = csched2_vcpu(idle_vcpu[cpu]);
}
else
- snext = runq_candidate(rqd, scurr, cpu, now, &skipped_vcpus);
+ snext = runq_candidate(rqd, scurr, cpu, now);
/* If switching from a non-idle runnable vcpu, put it
* back on the runqueue. */
@@ -3543,6 +3533,8 @@ csched2_schedule(
/* Accounting for non-idle tasks */
if ( !is_idle_vcpu(snext->vcpu) )
{
+ int top_credit;
+
/* If switching, remove this from the runqueue and mark it scheduled */
if ( snext != scurr )
{
@@ -3570,11 +3562,15 @@ csched2_schedule(
* 2) no other vcpu with higher credits wants to run.
*
* Here, where we want to check for reset, we need to make sure the
- * proper vcpu is being used. In fact, runqueue_candidate() may have
- * not returned the first vcpu in the runqueue, for various reasons
+ * proper vcpu is being used. In fact, runq_candidate() may have not
+ * returned the first vcpu in the runqueue, for various reasons
* (e.g., affinity). Only trigger a reset when it does.
*/
- if ( skipped_vcpus == 0 && snext->credit <= CSCHED2_CREDIT_RESET )
+ if ( list_empty(&rqd->runq) )
+ top_credit = snext->credit;
+ else
+ top_credit = max(snext->credit, runq_elem(rqd->runq.next)->credit);
+ if ( top_credit <= CSCHED2_CREDIT_RESET )
{
reset_credit(ops, cpu, now, snext);
balance_load(ops, cpu, now);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12
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