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

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Date:	Tue, 13 Jan 2015 09:14:22 +0100
From:	Imre Palik <imrep.amz@...il.com>
To:	xen-devel@...ts.xenproject.org,
	David Vrabel <david.vrabel@...rix.com>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, "Palik, Imre" <imrep@...zon.de>,
	Anthony Liguori <aliguori@...zon.com>
Subject: [PATCH] xen-time: decreasing the rating of the xen clocksource below that of the tsc clocksource for dom0's

From: "Palik, Imre" <imrep@...zon.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.

This patch decreases the rating of the Xen clocksource in Dom0s to 275.
Which is half-way between the rating of the TSC clocksource (300) and the
hpet clocksource (250).

Cc: Anthony Liguori <aliguori@...zon.com>
Signed-off-by: Imre Palik <imrep@...zon.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

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