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Date: Wed, 10 Dec 2014 18:29:43 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [QEMU patch 2/2] kvm: allow configuration of tsc
 deadline timer advancement
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To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, Luiz Capitulino <lcapitulino@redhat.com>



On 10/12/2014 18:27, Marcelo Tosatti wrote:
> On Wed, Dec 10, 2014 at 06:09:19PM +0100, Paolo Bonzini wrote:
>>
>>
>> On 10/12/2014 18:04, Marcelo Tosatti wrote:
>>>> Please add an object property to the x86 CPU object.  It can then be
>>>> configured with "-global" on the command line.
>>>
>>> Don't want to allow individual values for different CPUs. 
>>> It is a per-VM property.
>>
>> Why?  It can cause busy waiting, it would make sense to make it stricter
>> for realtime CPUs and leave 0 for non-realtime CPUs.
>>
>> Paolo
> 
> HW timer behaviour should be consistent across CPUs, IMO.

It's not going to be anyway.  Cache line bounces, frequency scaling,
presence of higher-priority RT tasks, etc. can cause different response
for one CPU over the others.

Paolo