[Xen-devel] [PATCH v6 16/20] xen/sched: support differing granularity in schedule_cpu_[add/rm]()

From: Juergen Gross <jgross@suse.com>
To: xen-devel@lists.xenproject.org
Cc: Juergen Gross <jgross@suse.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Dario Faggioli <dfaggioli@suse.com>
Subject: [Xen-devel] [PATCH v6 16/20] xen/sched: support differing granularity in schedule_cpu_[add/rm]()
Date: Wed,  2 Oct 2019 09:27:41 +0200	[thread overview]
Message-ID: <20191002072745.24919-17-jgross@suse.com> (raw)
In-Reply-To: <20191002072745.24919-1-jgross@suse.com>

With core scheduling active schedule_cpu_[add/rm]() has to cope with
different scheduling granularity: a cpu not in any cpupool is subject
to granularity 1 (cpu scheduling), while a cpu in a cpupool might be
in a scheduling resource with more than one cpu.

Handle that by having arrays of old/new pdata and vdata and loop over
those where appropriate.

Additionally the scheduling resource(s) must either be merged or
split.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>
---
 xen/common/cpupool.c  |  18 ++--
 xen/common/schedule.c | 226 +++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 204 insertions(+), 40 deletions(-)

diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c
index 13dffaadcf..04c3b3c04b 100644
--- a/xen/common/cpupool.c
+++ b/xen/common/cpupool.c
@@ -536,6 +536,7 @@ static void cpupool_cpu_remove(unsigned int cpu)
         ret = cpupool_unassign_cpu_finish(cpupool0);
         BUG_ON(ret);
     }
+    cpumask_clear_cpu(cpu, &cpupool_free_cpus);
 }
 
 /*
@@ -585,20 +586,19 @@ static void cpupool_cpu_remove_forced(unsigned int cpu)
     struct cpupool **c;
     int ret;
 
-    if ( cpumask_test_cpu(cpu, &cpupool_free_cpus) )
-        cpumask_clear_cpu(cpu, &cpupool_free_cpus);
-    else
+    for_each_cpupool ( c )
     {
-        for_each_cpupool(c)
+        if ( cpumask_test_cpu(cpu, (*c)->cpu_valid) )
         {
-            if ( cpumask_test_cpu(cpu, (*c)->cpu_valid) )
-            {
-                ret = cpupool_unassign_cpu(*c, cpu);
-                BUG_ON(ret);
-            }
+            ret = cpupool_unassign_cpu_start(*c, cpu);
+            BUG_ON(ret);
+            ret = cpupool_unassign_cpu_finish(*c);
+            BUG_ON(ret);
         }
     }
 
+    cpumask_clear_cpu(cpu, &cpupool_free_cpus);
+
     rcu_read_lock(&sched_res_rculock);
     sched_rm_cpu(cpu);
     rcu_read_unlock(&sched_res_rculock);
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index efe077b01f..e411b6d03e 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -425,27 +425,30 @@ static void sched_unit_add_vcpu(struct sched_unit *unit, struct vcpu *v)
     unit->runstate_cnt[v->runstate.state]++;
 }
 
-static struct sched_unit *sched_alloc_unit(struct vcpu *v)
+static struct sched_unit *sched_alloc_unit_mem(void)
 {
-    struct sched_unit *unit, **prev_unit;
-    struct domain *d = v->domain;
-    unsigned int gran = cpupool_get_granularity(d->cpupool);
+    struct sched_unit *unit;
 
-    for_each_sched_unit ( d, unit )
-        if ( unit->unit_id / gran == v->vcpu_id / gran )
-            break;
+    unit = xzalloc(struct sched_unit);
+    if ( !unit )
+        return NULL;
 
-    if ( unit )
+    if ( !zalloc_cpumask_var(&unit->cpu_hard_affinity) ||
+         !zalloc_cpumask_var(&unit->cpu_hard_affinity_saved) ||
+         !zalloc_cpumask_var(&unit->cpu_soft_affinity) )
     {
-        sched_unit_add_vcpu(unit, v);
-        return unit;
+        sched_free_unit_mem(unit);
+        unit = NULL;
     }
 
-    if ( (unit = xzalloc(struct sched_unit)) == NULL )
-        return NULL;
+    return unit;
+}
+
+static void sched_domain_insert_unit(struct sched_unit *unit, struct domain *d)
+{
+    struct sched_unit **prev_unit;
 
     unit->domain = d;
-    sched_unit_add_vcpu(unit, v);
 
     for ( prev_unit = &d->sched_unit_list; *prev_unit;
           prev_unit = &(*prev_unit)->next_in_list )
@@ -455,17 +458,31 @@ static struct sched_unit *sched_alloc_unit(struct vcpu *v)
 
     unit->next_in_list = *prev_unit;
     *prev_unit = unit;
+}
 
-    if ( !zalloc_cpumask_var(&unit->cpu_hard_affinity) ||
-         !zalloc_cpumask_var(&unit->cpu_hard_affinity_saved) ||
-         !zalloc_cpumask_var(&unit->cpu_soft_affinity) )
-        goto fail;
+static struct sched_unit *sched_alloc_unit(struct vcpu *v)
+{
+    struct sched_unit *unit;
+    struct domain *d = v->domain;
+    unsigned int gran = cpupool_get_granularity(d->cpupool);
 
-    return unit;
+    for_each_sched_unit ( d, unit )
+        if ( unit->unit_id / gran == v->vcpu_id / gran )
+            break;
 
- fail:
-    sched_free_unit(unit, v);
-    return NULL;
+    if ( unit )
+    {
+        sched_unit_add_vcpu(unit, v);
+        return unit;
+    }
+
+    if ( (unit = sched_alloc_unit_mem()) == NULL )
+        return NULL;
+
+    sched_unit_add_vcpu(unit, v);
+    sched_domain_insert_unit(unit, d);
+
+    return unit;
 }
 
 static unsigned int sched_select_initial_cpu(const struct vcpu *v)
@@ -2419,18 +2436,28 @@ static void poll_timer_fn(void *data)
         vcpu_unblock(v);
 }
 
-static int cpu_schedule_up(unsigned int cpu)
+static struct sched_resource *sched_alloc_res(void)
 {
     struct sched_resource *sr;
 
     sr = xzalloc(struct sched_resource);
     if ( sr == NULL )
-        return -ENOMEM;
+        return NULL;
     if ( !zalloc_cpumask_var(&sr->cpus) )
     {
         xfree(sr);
-        return -ENOMEM;
+        return NULL;
     }
+    return sr;
+}
+
+static int cpu_schedule_up(unsigned int cpu)
+{
+    struct sched_resource *sr;
+
+    sr = sched_alloc_res();
+    if ( sr == NULL )
+        return -ENOMEM;
 
     sr->master_cpu = cpu;
     cpumask_copy(sr->cpus, cpumask_of(cpu));
@@ -2480,6 +2507,8 @@ static void sched_res_free(struct rcu_head *head)
     struct sched_resource *sr = container_of(head, struct sched_resource, rcu);
 
     free_cpumask_var(sr->cpus);
+    if ( sr->sched_unit_idle )
+        sched_free_unit_mem(sr->sched_unit_idle);
     xfree(sr);
 }
 
@@ -2496,6 +2525,8 @@ static void cpu_schedule_down(unsigned int cpu)
     cpumask_clear_cpu(cpu, &sched_res_mask);
     set_sched_res(cpu, NULL);
 
+    /* Keep idle unit. */
+    sr->sched_unit_idle = NULL;
     call_rcu(&sr->rcu, sched_res_free);
 
     rcu_read_unlock(&sched_res_rculock);
@@ -2575,6 +2606,30 @@ static struct notifier_block cpu_schedule_nfb = {
     .notifier_call = cpu_schedule_callback
 };
 
+static const cpumask_t *sched_get_opt_cpumask(enum sched_gran opt,
+                                              unsigned int cpu)
+{
+    const cpumask_t *mask;
+
+    switch ( opt )
+    {
+    case SCHED_GRAN_cpu:
+        mask = cpumask_of(cpu);
+        break;
+    case SCHED_GRAN_core:
+        mask = per_cpu(cpu_sibling_mask, cpu);
+        break;
+    case SCHED_GRAN_socket:
+        mask = per_cpu(cpu_core_mask, cpu);
+        break;
+    default:
+        ASSERT_UNREACHABLE();
+        return NULL;
+    }
+
+    return mask;
+}
+
 /* Initialise the data structures. */
 void __init scheduler_init(void)
 {
@@ -2730,6 +2785,46 @@ int schedule_cpu_add(unsigned int cpu, struct cpupool *c)
      */
     old_lock = pcpu_schedule_lock_irqsave(cpu, &flags);
 
+    if ( cpupool_get_granularity(c) > 1 )
+    {
+        const cpumask_t *mask;
+        unsigned int cpu_iter, idx = 0;
+        struct sched_unit *old_unit, *master_unit;
+        struct sched_resource *sr_old;
+
+        /*
+         * We need to merge multiple idle_vcpu units and sched_resource structs
+         * into one. As the free cpus all share the same lock we are fine doing
+         * that now. The worst which could happen would be someone waiting for
+         * the lock, thus dereferencing sched_res->schedule_lock. This is the
+         * reason we are freeing struct sched_res via call_rcu() to avoid the
+         * lock pointer suddenly disappearing.
+         */
+        mask = sched_get_opt_cpumask(c->gran, cpu);
+        master_unit = idle_vcpu[cpu]->sched_unit;
+
+        for_each_cpu ( cpu_iter, mask )
+        {
+            if ( idx )
+                cpumask_clear_cpu(cpu_iter, &sched_res_mask);
+
+            per_cpu(sched_res_idx, cpu_iter) = idx++;
+
+            if ( cpu == cpu_iter )
+                continue;
+
+            old_unit = idle_vcpu[cpu_iter]->sched_unit;
+            sr_old = get_sched_res(cpu_iter);
+            kill_timer(&sr_old->s_timer);
+            idle_vcpu[cpu_iter]->sched_unit = master_unit;
+            master_unit->runstate_cnt[RUNSTATE_running]++;
+            set_sched_res(cpu_iter, sr);
+            cpumask_set_cpu(cpu_iter, sr->cpus);
+
+            call_rcu(&sr_old->rcu, sched_res_free);
+        }
+    }
+
     new_lock = sched_switch_sched(new_ops, cpu, ppriv, vpriv);
 
     sr->scheduler = new_ops;
@@ -2767,33 +2862,100 @@ out:
  */
 int schedule_cpu_rm(unsigned int cpu)
 {
-    struct vcpu *idle;
     void *ppriv_old, *vpriv_old;
-    struct sched_resource *sr;
+    struct sched_resource *sr, **sr_new = NULL;
+    struct sched_unit *unit;
     struct scheduler *old_ops;
     spinlock_t *old_lock;
     unsigned long flags;
+    int idx, ret = -ENOMEM;
+    unsigned int cpu_iter;
 
     rcu_read_lock(&sched_res_rculock);
 
     sr = get_sched_res(cpu);
     old_ops = sr->scheduler;
 
+    if ( sr->granularity > 1 )
+    {
+        sr_new = xmalloc_array(struct sched_resource *, sr->granularity - 1);
+        if ( !sr_new )
+            goto out;
+        for ( idx = 0; idx < sr->granularity - 1; idx++ )
+        {
+            sr_new[idx] = sched_alloc_res();
+            if ( sr_new[idx] )
+            {
+                sr_new[idx]->sched_unit_idle = sched_alloc_unit_mem();
+                if ( !sr_new[idx]->sched_unit_idle )
+                {
+                    sched_res_free(&sr_new[idx]->rcu);
+                    sr_new[idx] = NULL;
+                }
+            }
+            if ( !sr_new[idx] )
+            {
+                for ( idx--; idx >= 0; idx-- )
+                    sched_res_free(&sr_new[idx]->rcu);
+                goto out;
+            }
+            sr_new[idx]->curr = sr_new[idx]->sched_unit_idle;
+            sr_new[idx]->scheduler = &sched_idle_ops;
+            sr_new[idx]->granularity = 1;
+
+            /* We want the lock not to change when replacing the resource. */
+            sr_new[idx]->schedule_lock = sr->schedule_lock;
+        }
+    }
+
+    ret = 0;
     ASSERT(sr->cpupool != NULL);
     ASSERT(cpumask_test_cpu(cpu, &cpupool_free_cpus));
     ASSERT(!cpumask_test_cpu(cpu, sr->cpupool->cpu_valid));
 
-    idle = idle_vcpu[cpu];
-
     sched_do_tick_suspend(old_ops, cpu);
 
     /* See comment in schedule_cpu_add() regarding lock switching. */
     old_lock = pcpu_schedule_lock_irqsave(cpu, &flags);
 
-    vpriv_old = idle->sched_unit->priv;
+    vpriv_old = idle_vcpu[cpu]->sched_unit->priv;
     ppriv_old = sr->sched_priv;
 
-    idle->sched_unit->priv = NULL;
+    idx = 0;
+    for_each_cpu ( cpu_iter, sr->cpus )
+    {
+        per_cpu(sched_res_idx, cpu_iter) = 0;
+        if ( cpu_iter == cpu )
+        {
+            idle_vcpu[cpu_iter]->sched_unit->priv = NULL;
+        }
+        else
+        {
+            /* Initialize unit. */
+            unit = sr_new[idx]->sched_unit_idle;
+            unit->res = sr_new[idx];
+            unit->is_running = true;
+            sched_unit_add_vcpu(unit, idle_vcpu[cpu_iter]);
+            sched_domain_insert_unit(unit, idle_vcpu[cpu_iter]->domain);
+
+            /* Adjust cpu masks of resources (old and new). */
+            cpumask_clear_cpu(cpu_iter, sr->cpus);
+            cpumask_set_cpu(cpu_iter, sr_new[idx]->cpus);
+
+            /* Init timer. */
+            init_timer(&sr_new[idx]->s_timer, s_timer_fn, NULL, cpu_iter);
+
+            /* Last resource initializations and insert resource pointer. */
+            sr_new[idx]->master_cpu = cpu_iter;
+            set_sched_res(cpu_iter, sr_new[idx]);
+
+            /* Last action: set the new lock pointer. */
+            smp_mb();
+            sr_new[idx]->schedule_lock = &sched_free_cpu_lock;
+
+            idx++;
+        }
+    }
     sr->scheduler = &sched_idle_ops;
     sr->sched_priv = NULL;
 
@@ -2811,9 +2973,11 @@ int schedule_cpu_rm(unsigned int cpu)
     sr->granularity = 1;
     sr->cpupool = NULL;
 
+out:
     rcu_read_unlock(&sched_res_rculock);
+    xfree(sr_new);
 
-    return 0;
+    return ret;
 }
 
 struct scheduler *scheduler_get_default(void)
-- 
2.16.4


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