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

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Message-ID: <DE8DF0795D48FD4CA783C40EC8292335322311@SHSMSX101.ccr.corp.intel.com>
Date:	Fri, 7 Sep 2012 12:07:02 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, kvm <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] KVM: tsc deadline timer works only when hrtimer high
 resolution configured

Avi Kivity wrote:
>> 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;
> 
> I prefer a patch making kvm for x86 depend on hrtimers.  kvm already
> provides a high resolution timer to the guest in the local apic,
> backing it with the jiffies event source will likely cause some
> guests to malfunction.

Yep, I did a draft test for kvm lapic timer, it also worked fail when CONFIG_HIGH_RES_TIMERS disabled.

Attached is the udpated patch.

Thanks,
Jinsong

====================
>From 64d0458ec50a7d6917adf1e9735ba6e6ae6024ad Mon Sep 17 00:00:00 2001
From: Liu, Jinsong <jinsong.liu@...el.com>
Date: Sat, 8 Sep 2012 03:32:31 +0800
Subject: [PATCH] KVM: select HIGH_RES_TIMERS when KVM enabled

This is for 2 reasons:
1. it's pointless for kvm lapic timer and tsc deadline timer
when kernel hrtimer not configured as high resolution, since
that would be not accurate based on wheel;
2. kvm lapic timer and 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 then make kvm lapic timer and tsc deadline timer fail.

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

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index a28f338..5f861ca 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -24,6 +24,8 @@ config KVM
 	depends on PCI
 	# for TASKSTATS/TASK_DELAY_ACCT:
 	depends on NET
+	# for HIGH_RES_TIMERS
+	depends on !ARCH_USES_GETTIMEOFFSET
 	select PREEMPT_NOTIFIERS
 	select MMU_NOTIFIER
 	select ANON_INODES
@@ -37,6 +39,8 @@ config KVM
 	select TASK_DELAY_ACCT
 	select PERF_EVENTS
 	select HAVE_KVM_MSI
+	select GENERIC_CLOCKEVENTS
+	select HIGH_RES_TIMERS
 	---help---
 	  Support hosting fully virtualized guest machines using hardware
 	  virtualization extensions.  You will need a fairly recent
-- 
1.7.1

Download attachment "0001-KVM-select-HIGH_RES_TIMERS-when-KVM-enabled.patch" of type "application/octet-stream" (1488 bytes)