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

From: Imre Palik
Date: Wed Jan 07 2015 - 11:17:55 EST


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) {
--
1.7.9.5

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