From: Anthony Liguori <anthony@codemonkey.ws>
To: Joerg Roedel <joro@8bytes.org>
Cc: Anthony Liguori <aliguori@us.ibm.com>,
kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Chris Wright <chrisw@sous-sol.org>,
Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Subject: Re: [PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v3)
Date: Fri, 03 Dec 2010 17:38:06 -0600 [thread overview]
Message-ID: <4CF97F5E.3000704@codemonkey.ws> (raw)
In-Reply-To: <20101203233231.GA29502@8bytes.org>
On 12/03/2010 05:32 PM, Joerg Roedel wrote:
> On Fri, Dec 03, 2010 at 04:39:22PM -0600, Anthony Liguori wrote:
>
>> + if (yield_on_hlt)
>> + min |= CPU_BASED_HLT_EXITING;
>>
> This approach won't work out on AMD because in HLT the CPU may enter
> C1e. In C1e the local apic timer interupt is not delivered anymore and
> when this is the current timer in use the cpu may miss timer ticks or
> never comes out of HLT again. The guest has no chance to work around
> this as the Linux idle routine does.
>
And this doesn't break old software on bare metal?
Regards,
Anthony Liguori
> If you really wan't active idling of a guest, it should idle in the
> hypervisor where it can work around such problems.
>
> Joerg
>
> --
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>
next prev parent reply other threads:[~2010-12-03 23:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-03 22:39 [PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v3) Anthony Liguori
2010-12-03 23:32 ` Joerg Roedel
2010-12-03 23:38 ` Anthony Liguori [this message]
2010-12-04 8:53 ` Joerg Roedel
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