[Xen-changelog] [xen stable-4.2] x86/S3: Fix cpu pool scheduling after suspend/resume

[patchbot@xxxxxxx]

commit 7fe762b3f06f0e81ce5b3456dc61fc004562ef21
Author:     Ben Guthro <benjamin.guthro@xxxxxxxxxx>
AuthorDate: Mon Apr 29 16:08:16 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Apr 29 16:08:16 2013 +0200

    x86/S3: Fix cpu pool scheduling after suspend/resume
    
    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
    
    Signed-off-by: Ben Guthro <benjamin.guthro@xxxxxxxxxx>
    Acked-by: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
    master commit: 9aa356bc9f7533c3cb7f02c823f532532876d444
    master date: 2013-04-19 12:29:01 +0200
---
 xen/common/cpupool.c       |   56 +++++++++++++++++++++++++++++++++++--------
 xen/include/xen/sched-if.h |    1 +
 2 files changed, 46 insertions(+), 11 deletions(-)

diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c
index c036c2c..637f56c 100644
--- a/xen/common/cpupool.c
+++ b/xen/common/cpupool.c
@@ -41,16 +41,28 @@ static struct cpupool *alloc_cpupool_struct(void)
 {
     struct cpupool *c = xzalloc(struct cpupool);
 
-    if ( c && zalloc_cpumask_var(&c->cpu_valid) )
-        return c;
-    xfree(c);
-    return NULL;
+    if ( !c || !zalloc_cpumask_var(&c->cpu_valid) )
+    {
+        xfree(c);
+        c = NULL;
+    }
+    else if ( !zalloc_cpumask_var(&c->cpu_suspended) )
+    {
+        free_cpumask_var(c->cpu_valid);
+        xfree(c);
+        c = NULL;
+    }
+
+    return c;
 }
 
 static void free_cpupool_struct(struct cpupool *c)
 {
     if ( c )
+    {
+        free_cpumask_var(c->cpu_suspended);
         free_cpumask_var(c->cpu_valid);
+    }
     xfree(c);
 }
 
@@ -417,14 +429,32 @@ 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)
 {
     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 )
+    {
+        struct cpupool **c;
+
+        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 +466,7 @@ 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;
@@ -633,9 +663,14 @@ static int cpu_callback(
     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 )
+    {
+        struct cpupool **c;
+
+        for_each_cpupool(c)
+            if ( cpumask_test_cpu(cpu, (*c)->cpu_valid ) )
+                cpumask_set_cpu(cpu, (*c)->cpu_suspended);
+    }
 
     switch ( action )
     {
@@ -650,7 +685,6 @@ 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 bd6186a..c3be9dc 100644
--- a/xen/include/xen/sched-if.h
+++ b/xen/include/xen/sched-if.h
@@ -199,6 +199,7 @@ 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;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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