linux-kernel - [PATCH] KVM: tsc deadline timer works only when hrtimer high resolution configured

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Message-ID: <DE8DF0795D48FD4CA783C40EC829233531F0E4@SHSMSX101.ccr.corp.intel.com>
Date:	Tue, 4 Sep 2012 15:07:00 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>, Avi Kivity <avi@...hat.com>,
	kvm <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] KVM: tsc deadline timer works only when hrtimer high
 resolution configured

>From 728a17e2de591b557c3c8ba31076b4bf2ca5ab42 Mon Sep 17 00:00:00 2001
From: Liu, Jinsong <jinsong.liu@...el.com>
Date: Wed, 5 Sep 2012 03:18:15 +0800
Subject: [PATCH] KVM: tsc deadline timer works only when hrtimer high resolution configured

This is for 2 reasons:
1. it's pointless to enable tsc deadline timer to guest when kernel hrtimer
not configured as high resolution, since that would be un-precise based on wheel;
2. tsc deadline timer based on hrtimer, setting a leftmost node to rb tree
and then do hrtimer reprogram. If hrtimer not configured as high resolution,
hrtimer_enqueue_reprogram do nothing and would make tsc deadline timer fail.

Signed-off-by: Liu, Jinsong <jinsong.liu@...el.com>
---
 arch/x86/kvm/x86.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 148ed66..0e64997 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2210,7 +2210,11 @@ int kvm_dev_ioctl_check_extension(long ext)
 		r = kvm_has_tsc_control;
 		break;
 	case KVM_CAP_TSC_DEADLINE_TIMER:
+#ifdef CONFIG_HIGH_RES_TIMERS
 		r = boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER);
+#else
+		r = 0;
+#endif
 		break;
 	default:
 		r = 0;
-- 
1.7.1

Download attachment "0001-KVM-tsc-deadline-timer-works-only-when-hrtimer-high-.patch" of type "application/octet-stream" (1218 bytes)