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

[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

Signed-off-by: Ben Guthro <benjamin.guthro@xxxxxxxxxx>
---
 xen/common/cpu.c     |    3 +++
 xen/common/cpupool.c |    5 -----
 2 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/xen/common/cpu.c b/xen/common/cpu.c
index 630881e..e20868c 100644
--- a/xen/common/cpu.c
+++ b/xen/common/cpu.c
@@ -5,6 +5,7 @@
 #include <xen/init.h>
 #include <xen/sched.h>
 #include <xen/stop_machine.h>
+#include <xen/sched-if.h>
 
 unsigned int __read_mostly nr_cpu_ids = NR_CPUS;
 #ifndef nr_cpumask_bits
@@ -212,6 +213,8 @@ void enable_nonboot_cpus(void)
             BUG_ON(error == -EBUSY);
             printk("Error taking CPU%d up: %d\n", cpu, error);
         }
+        if (system_state == SYS_STATE_resume)
+            cpumask_set_cpu(cpu, cpupool0->cpu_valid);
     }
 
     cpumask_clear(&frozen_cpus);
diff --git a/xen/common/cpupool.c b/xen/common/cpupool.c
index 10b10f8..a9653a8 100644
--- a/xen/common/cpupool.c
+++ b/xen/common/cpupool.c
@@ -633,10 +633,6 @@ 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;
-
     switch ( action )
     {
     case CPU_DOWN_FAILED:
@@ -650,7 +646,6 @@ static int cpu_callback(
         break;
     }
 
-out:
     return !rc ? NOTIFY_DONE : notifier_from_errno(rc);
 }
 
-- 
1.7.9.5


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