[Xen-devel] [PATCH v2 30/48] xen/sched: introduce unit_runnable_state()

[Juergen Gross <jgross@suse.com>]

Today the vcpu runstate of a new scheduled vcpu is always set to
"running" even if at that time vcpu_runnable() is already returning
false due to a race (e.g. with pausing the vcpu).

With core scheduling this can no longer work as not all vcpus of a
schedule unit have to be "running" when being scheduled. So the vcpu's
new runstate has to be selected at the same time as the runnability of
the related schedule unit is probed.

For this purpose introduce a new helper unit_runnable_state() which
will save the new runstate of all tested vcpus in a new field of the
vcpu struct.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
RFC V2: new patch
---
 xen/common/domain.c         |  1 +
 xen/common/sched_arinc653.c |  2 +-
 xen/common/sched_credit.c   | 49 ++++++++++++++++++++++++---------------------
 xen/common/sched_credit2.c  |  7 ++++---
 xen/common/sched_null.c     |  3 ++-
 xen/common/sched_rt.c       |  8 +++++++-
 xen/common/schedule.c       |  2 +-
 xen/include/xen/sched-if.h  | 14 +++++++++++++
 xen/include/xen/sched.h     |  1 +
 9 files changed, 57 insertions(+), 30 deletions(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 863b7cae35..3797f954f5 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -157,6 +157,7 @@ struct vcpu *vcpu_create(struct domain *d, unsigned int vcpu_id)
     if ( is_idle_domain(d) )
     {
         v->runstate.state = RUNSTATE_running;
+        v->new_state = RUNSTATE_running;
     }
     else
     {
diff --git a/xen/common/sched_arinc653.c b/xen/common/sched_arinc653.c
index 34efcc07c9..759c42ab73 100644
--- a/xen/common/sched_arinc653.c
+++ b/xen/common/sched_arinc653.c
@@ -557,7 +557,7 @@ a653sched_do_schedule(
     if ( !((new_task != NULL)
            && (AUNIT(new_task) != NULL)
            && AUNIT(new_task)->awake
-           && unit_runnable(new_task)) )
+           && unit_runnable_state(new_task)) )
         new_task = IDLETASK(cpu);
     BUG_ON(new_task == NULL);
 
diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index f1675fd52e..aeb659577e 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -1894,7 +1894,7 @@ static void csched_schedule(
     if ( !test_bit(CSCHED_FLAG_UNIT_YIELD, &scurr->flags)
          && !tasklet_work_scheduled
          && prv->ratelimit
-         && unit_runnable(unit)
+         && unit_runnable_state(unit)
          && !is_idle_unit(unit)
          && runtime < prv->ratelimit )
     {
@@ -1939,33 +1939,36 @@ static void csched_schedule(
         dec_nr_runnable(sched_cpu);
     }
 
-    snext = __runq_elem(runq->next);
-
-    /* Tasklet work (which runs in idle UNIT context) overrides all else. */
-    if ( tasklet_work_scheduled )
-    {
-        TRACE_0D(TRC_CSCHED_SCHED_TASKLET);
-        snext = CSCHED_UNIT(sched_idle_unit(sched_cpu));
-        snext->pri = CSCHED_PRI_TS_BOOST;
-    }
-
     /*
      * Clear YIELD flag before scheduling out
      */
     clear_bit(CSCHED_FLAG_UNIT_YIELD, &scurr->flags);
 
-    /*
-     * SMP Load balance:
-     *
-     * If the next highest priority local runnable UNIT has already eaten
-     * through its credits, look on other PCPUs to see if we have more
-     * urgent work... If not, csched_load_balance() will return snext, but
-     * already removed from the runq.
-     */
-    if ( snext->pri > CSCHED_PRI_TS_OVER )
-        __runq_remove(snext);
-    else
-        snext = csched_load_balance(prv, sched_cpu, snext, &migrated);
+    do {
+        snext = __runq_elem(runq->next);
+
+        /* Tasklet work (which runs in idle UNIT context) overrides all else. */
+        if ( tasklet_work_scheduled )
+        {
+            TRACE_0D(TRC_CSCHED_SCHED_TASKLET);
+            snext = CSCHED_UNIT(sched_idle_unit(sched_cpu));
+            snext->pri = CSCHED_PRI_TS_BOOST;
+        }
+
+        /*
+         * SMP Load balance:
+         *
+         * If the next highest priority local runnable UNIT has already eaten
+         * through its credits, look on other PCPUs to see if we have more
+         * urgent work... If not, csched_load_balance() will return snext, but
+         * already removed from the runq.
+         */
+        if ( snext->pri > CSCHED_PRI_TS_OVER )
+            __runq_remove(snext);
+        else
+            snext = csched_load_balance(prv, sched_cpu, snext, &migrated);
+
+    } while ( !unit_runnable_state(snext->unit) );
 
     /*
      * Update idlers mask if necessary. When we're idling, other CPUs
diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 98ef48d6f4..af06d02056 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -3289,7 +3289,7 @@ runq_candidate(struct csched2_runqueue_data *rqd,
      * In fact, it may be the case that scurr is about to spin, and there's
      * no point forcing it to do so until rate limiting expires.
      */
-    if ( !yield && prv->ratelimit_us && unit_runnable(scurr->unit) &&
+    if ( !yield && prv->ratelimit_us && unit_runnable_state(scurr->unit) &&
          (now - scurr->unit->state_entry_time) < MICROSECS(prv->ratelimit_us) )
     {
         if ( unlikely(tb_init_done) )
@@ -3343,7 +3343,7 @@ runq_candidate(struct csched2_runqueue_data *rqd,
      *
      * Of course, we also default to idle also if scurr is not runnable.
      */
-    if ( unit_runnable(scurr->unit) && !soft_aff_preempt )
+    if ( unit_runnable_state(scurr->unit) && !soft_aff_preempt )
         snext = scurr;
     else
         snext = csched2_unit(sched_idle_unit(cpu));
@@ -3403,7 +3403,8 @@ runq_candidate(struct csched2_runqueue_data *rqd,
          * some budget, then choose it.
          */
         if ( (yield || svc->credit > snext->credit) &&
-             (!has_cap(svc) || unit_grab_budget(svc)) )
+             (!has_cap(svc) || unit_grab_budget(svc)) &&
+             unit_runnable_state(svc->unit) )
             snext = svc;
 
         /* In any case, if we got this far, break. */
diff --git a/xen/common/sched_null.c b/xen/common/sched_null.c
index 397edcbc83..755d3e448c 100644
--- a/xen/common/sched_null.c
+++ b/xen/common/sched_null.c
@@ -864,7 +864,8 @@ static void null_schedule(const struct scheduler *ops, struct sched_unit *prev,
             cpumask_set_cpu(cpu, &prv->cpus_free);
     }
 
-    if ( unlikely(prev->next_task == NULL || !unit_runnable(prev->next_task)) )
+    if ( unlikely(prev->next_task == NULL ||
+                  !unit_runnable_state(prev->next_task)) )
         prev->next_task = sched_idle_unit(sched_cpu);
 
     NULL_UNIT_CHECK(prev->next_task);
diff --git a/xen/common/sched_rt.c b/xen/common/sched_rt.c
index fcbfa528f4..205ff13c09 100644
--- a/xen/common/sched_rt.c
+++ b/xen/common/sched_rt.c
@@ -1093,12 +1093,18 @@ rt_schedule(const struct scheduler *ops, struct sched_unit *currunit,
     else
     {
         snext = runq_pick(ops, cpumask_of(sched_cpu));
+
         if ( snext == NULL )
             snext = rt_unit(sched_idle_unit(sched_cpu));
+        else if ( !unit_runnable_state(snext->unit) )
+        {
+            q_remove(snext);
+            snext = rt_unit(sched_idle_unit(sched_cpu));
+        }
 
         /* if scurr has higher priority and budget, still pick scurr */
         if ( !is_idle_unit(currunit) &&
-             unit_runnable(currunit) &&
+             unit_runnable_state(currunit) &&
              scurr->cur_budget > 0 &&
              ( is_idle_unit(snext->unit) ||
                compare_unit_priority(scurr, snext) > 0 ) )
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 0160c30465..2ecb76e3b9 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -266,7 +266,7 @@ static inline void sched_unit_runstate_change(struct sched_unit *unit,
     struct vcpu *v = unit->vcpu_list;
 
     if ( running )
-        vcpu_runstate_change(v, RUNSTATE_running, new_entry_time);
+        vcpu_runstate_change(v, v->new_state, new_entry_time);
     else
         vcpu_runstate_change(v,
             ((v->pause_flags & VPF_blocked) ? RUNSTATE_blocked :
diff --git a/xen/include/xen/sched-if.h b/xen/include/xen/sched-if.h
index f810a9fba1..aa896f49ef 100644
--- a/xen/include/xen/sched-if.h
+++ b/xen/include/xen/sched-if.h
@@ -75,6 +75,20 @@ static inline bool unit_runnable(const struct sched_unit *unit)
     return vcpu_runnable(unit->vcpu_list);
 }
 
+static inline bool unit_runnable_state(const struct sched_unit *unit)
+{
+    struct vcpu *v;
+    bool runnable;
+
+    v = unit->vcpu_list;
+    runnable = vcpu_runnable(v);
+
+    v->new_state = runnable ? RUNSTATE_running
+                            : (v->pause_flags & VPF_blocked)
+                              ? RUNSTATE_blocked : RUNSTATE_offline;
+    return runnable;
+}
+
 static inline void sched_set_res(struct sched_unit *unit,
                                  struct sched_resource *res)
 {
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 8f4e389b3b..7585bd81a2 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -174,6 +174,7 @@ struct vcpu
         XEN_GUEST_HANDLE(vcpu_runstate_info_compat_t) compat;
     } runstate_guest; /* guest address */
 #endif
+    int              new_state;
 
     /* Has the FPU been initialised? */
     bool             fpu_initialised;
-- 
2.16.4


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