From: Avi Kivity <avi@redhat.com>
To: "Liu, Jinsong" <jinsong.liu@intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>, kvm <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: tsc deadline timer works only when hrtimer high resolution configured
Date: Thu, 06 Sep 2012 16:58:32 +0300 [thread overview]
Message-ID: <5048AC08.5050100@redhat.com> (raw)
In-Reply-To: <DE8DF0795D48FD4CA783C40EC829233531F0E4@SHSMSX101.ccr.corp.intel.com>
On 09/04/2012 06:07 PM, Liu, Jinsong wrote:
> From 728a17e2de591b557c3c8ba31076b4bf2ca5ab42 Mon Sep 17 00:00:00 2001
> From: Liu, Jinsong <jinsong.liu@intel.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.
>
>
> 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.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2012-09-06 13:58 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-04 15:07 [PATCH] KVM: tsc deadline timer works only when hrtimer high resolution configured Liu, Jinsong
2012-09-06 13:58 ` Avi Kivity [this message]
2012-09-07 12:07 ` Liu, Jinsong
2012-09-09 14:28 ` Avi Kivity
2012-09-09 14:54 ` Liu, Jinsong
2012-09-09 14:59 ` Avi Kivity
2012-09-09 15:10 ` Liu, Jinsong
2012-09-10 8:10 ` Avi Kivity
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