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[Xen-devel] [PATCH RFC] xen-time: decreasing the rating of the xen clocksource below that of the tsc clocksource for dom0's

From: "Palik, Imre" <imrep@xxxxxxxxx>

In Dom0's the use of the TSC clocksource (whenever it is stable enough to
be used) instead of the Xen clocksource should not cause any issues, as
Dom0 VMs never live-migrated.  The TSC clocksource is somewhat more
efficient than the Xen paravirtualised clocksource, thus it should have
higher rating.

Cc: Anthony Liguori <aliguori@xxxxxxxxxx>
Signed-off-by: Imre Palik <imrep@xxxxxxxxx>
 arch/x86/xen/time.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index f473d26..c768726 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -487,6 +487,10 @@ static void __init xen_time_init(void)
        int cpu = smp_processor_id();
        struct timespec tp;
+       /* As Dom0 is never moved, no penalty on using TSC there */
+       if (xen_initial_domain())
+               xen_clocksource.rating = 275;
        clocksource_register_hz(&xen_clocksource, NSEC_PER_SEC);
        if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL) == 0) {

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