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

From: Imre Palik <imrep.amz@gmail.com>
To: xen-devel@lists.xenproject.org
Cc: "Palik, Imre" <imrep@amazon.de>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	David Vrabel <david.vrabel@citrix.com>,
	Anthony Liguori <aliguori@amazon.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH RFC] xen-time: decreasing the rating of the xen clocksource below that of the tsc clocksource for dom0's
Date: Wed,  7 Jan 2015 17:16:38 +0100	[thread overview]
Message-ID: <1420647398-20207-1-git-send-email-imrep.amz__18135.945351287$1420647665$gmane$org@gmail.com> (raw)

From: "Palik, Imre" <imrep@amazon.de>

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@amazon.com>
Signed-off-by: Imre Palik <imrep@amazon.de>
---
 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
