[Xen-devel] [PATCH] x86/S3: Fix cpu pool scheduling after suspend/resume (v3)

[Ben Guthro <benjamin.guthro@xxxxxxxxxx>]

This review is another S3 scheduler problem with the system_state variable 
introduced with the following changeset:
http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=269f543ea750ed567d18f2e819e5d5ce58eda5c5

Specifically, the cpu_callback function that takes the CPU down during suspend, 
and back up during resume.
We were seeing situations where, after S3, only CPU0 was in cpupool0. Guest 
performance suffered greatly, since all vcpus were only on a single pcpu. 
Guests under high CPU load showed the problem much more quickly than an idle 
guest.

Removing this if condition forces the CPUs to go through the expected 
online/offline state, and be properly scheduled after S3.

This also includes a necessary partial change proposed earlier by Tomasz 
Wroblewski here:
http://lists.xen.org/archives/html/xen-devel/2013-01/msg02206.html

It should also resolve the issues discussed in this thread:
http://lists.xen.org/archives/html/xen-devel/2012-11/msg01801.html

v2:
Address concerns from Juergen Gross about the cpus not being put back into the 
pool they were in prior to suspend

v3:
Addressed leak of cpu_suspended, clean up hard tabs

Signed-off-by: Ben Guthro <benjamin.guthro@xxxxxxxxxx>
---
 xen/common/cpupool.c       |   57 ++++++++++++++++++++++++++++++++++----------
 xen/include/xen/sched-if.h |    1 +
 2 files changed, 46 insertions(+), 12 deletions(-)

diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c
index 10b10f8..6b5a3db 100644
--- a/xen/common/cpupool.c
+++ b/xen/common/cpupool.c
@@ -40,17 +40,31 @@ DEFINE_PER_CPU(struct cpupool *, cpupool);
 static struct cpupool *alloc_cpupool_struct(void)
 {
     struct cpupool *c = xzalloc(struct cpupool);
+    if ( !c )
+        return NULL;
 
-    if ( c && zalloc_cpumask_var(&c->cpu_valid) )
-        return c;
-    xfree(c);
-    return NULL;
+    if ( !zalloc_cpumask_var(&c->cpu_suspended) )
+    {
+        xfree(c);
+        return NULL;
+    }
+
+    if ( !zalloc_cpumask_var(&c->cpu_valid) )
+    {
+        free_cpumask_var(c->cpu_suspended);
+        xfree(c);
+        return NULL;
+    }
+
+    return c;
 }
 
 static void free_cpupool_struct(struct cpupool *c)
 {
-    if ( c )
+    if ( c ) {
+        free_cpumask_var(c->cpu_suspended);
         free_cpumask_var(c->cpu_valid);
+    }
     xfree(c);
 }
 
@@ -417,14 +431,32 @@ void cpupool_rm_domain(struct domain *d)
 
 /*
  * called to add a new cpu to pool admin
- * we add a hotplugged cpu to the cpupool0 to be able to add it to dom0
+ * we add a hotplugged cpu to the cpupool0 to be able to add it to dom0,
+ * unless we are resuming from S3, in which case we put the cpu back
+ * in the cpupool it was in prior to suspend.
  */
 static void cpupool_cpu_add(unsigned int cpu)
 {
+    struct cpupool **c;
     spin_lock(&cpupool_lock);
+
     cpumask_clear_cpu(cpu, &cpupool_locked_cpus);
     cpumask_set_cpu(cpu, &cpupool_free_cpus);
-    cpupool_assign_cpu_locked(cpupool0, cpu);
+
+    if ( system_state == SYS_STATE_resume )
+    {
+        for_each_cpupool(c)
+        {
+            if ( cpumask_test_cpu(cpu, (*c)->cpu_suspended ) )
+            {
+                cpupool_assign_cpu_locked((*c), cpu);
+                cpumask_clear_cpu(cpu, (*c)->cpu_suspended);
+            }
+        }
+    }
+
+    if ( cpumask_test_cpu(cpu, &cpupool_free_cpus) )
+        cpupool_assign_cpu_locked(cpupool0, cpu);
     spin_unlock(&cpupool_lock);
 }
 
@@ -436,7 +468,7 @@ static void cpupool_cpu_add(unsigned int cpu)
 static int cpupool_cpu_remove(unsigned int cpu)
 {
     int ret = 0;
-       
+
     spin_lock(&cpupool_lock);
     if ( !cpumask_test_cpu(cpu, cpupool0->cpu_valid))
         ret = -EBUSY;
@@ -630,12 +662,14 @@ void dump_runq(unsigned char key)
 static int cpu_callback(
     struct notifier_block *nfb, unsigned long action, void *hcpu)
 {
+    struct cpupool **c;
     unsigned int cpu = (unsigned long)hcpu;
     int rc = 0;
 
-    if ( (system_state == SYS_STATE_suspend) ||
-         (system_state == SYS_STATE_resume) )
-        goto out;
+    if ( system_state == SYS_STATE_suspend )
+        for_each_cpupool(c)
+            if ( cpumask_test_cpu(cpu, (*c)->cpu_valid ) )
+                cpumask_set_cpu(cpu, (*c)->cpu_suspended);
 
     switch ( action )
     {
@@ -650,7 +684,6 @@ static int cpu_callback(
         break;
     }
 
-out:
     return !rc ? NOTIFY_DONE : notifier_from_errno(rc);
 }
 
diff --git a/xen/include/xen/sched-if.h b/xen/include/xen/sched-if.h
index 9ace22c..84bb13f 100644
--- a/xen/include/xen/sched-if.h
+++ b/xen/include/xen/sched-if.h
@@ -201,6 +201,7 @@ struct cpupool
 {
     int              cpupool_id;
     cpumask_var_t    cpu_valid;      /* all cpus assigned to pool */
+    cpumask_var_t    cpu_suspended;  /* cpus in S3 that should be in this pool 
*/
     struct cpupool   *next;
     unsigned int     n_dom;
     struct scheduler *sched;
-- 
1.7.9.5


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