xen: yield to IPI target if necessary

When sending a call-function IPI to a vcpu, yield if the vcpu isn't
running.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 557b8e24706a..865953e6f341 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -360,7 +360,8 @@ int xen_smp_call_function_mask(cpumask_t mask, void (*func)(void *),
                                void *info, int wait)
 {
         struct call_data_struct data;
-        int cpus;
+        int cpus, cpu;
+        bool yield;
 
         /* Holding any lock stops cpus from going down. */
         spin_lock(&call_lock);
@@ -389,9 +390,14 @@ int xen_smp_call_function_mask(cpumask_t mask, void (*func)(void *),
         /* Send a message to other CPUs and wait for them to respond */
         xen_send_IPI_mask(mask, XEN_CALL_FUNCTION_VECTOR);
 
-        /* Make sure other vcpus get a chance to run.
-           XXX too severe?  Maybe we should check the other CPU's states? */
-        HYPERVISOR_sched_op(SCHEDOP_yield, 0);
+        /* Make sure other vcpus get a chance to run if they need to. */
+        yield = false;
+        for_each_cpu_mask(cpu, mask)
+                if (xen_vcpu_stolen(cpu))
+                        yield = true;
+
+        if (yield)
+                HYPERVISOR_sched_op(SCHEDOP_yield, 0);
 
         /* Wait for response */
         while (atomic_read(&data.started) != cpus ||