x86/xen/time: set pvclock flags on xen_time_init()

commit b888808093113ae7d63d213272d01fea4b8329ed upstream.

Specifically check for PVCLOCK_TSC_STABLE_BIT and if this bit is set,
then set it too on pvclock flags. This allows Xen clocksource to use it
and thus speeding up xen_clocksource_read() callers (i.e. sched_clock())

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 80c2a4b..5687be6 100644 (file)
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -373,6 +373,7 @@ static const struct pv_time_ops xen_time_ops __initconst = {
 
 static void __init xen_time_init(void)
 {
+       struct pvclock_vcpu_time_info *pvti;
        int cpu = smp_processor_id();
        struct timespec tp;
 
@@ -396,6 +397,14 @@ static void __init xen_time_init(void)
 
        setup_force_cpu_cap(X86_FEATURE_TSC);
 
+       /*
+        * We check ahead on the primary time info if this
+        * bit is supported hence speeding up Xen clocksource.
+        */
+       pvti = &__this_cpu_read(xen_vcpu)->time;
+       if (pvti->flags & PVCLOCK_TSC_STABLE_BIT)
+               pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
+
        xen_setup_runstate_info(cpu);
        xen_setup_timer(cpu);
        xen_setup_cpu_clockevents();