Re: [Qemu-devel] [QEMU patch 2/2] kvm: allow configuration of tsc deadline timer advancement

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/12/2014 18:35, Marcelo Tosatti wrote:
> On Wed, Dec 10, 2014 at 06:29:43PM +0100, Paolo Bonzini wrote:
>>
>>
>> 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.
>>>
>>> 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.
> 
> OK i'll change it to per-CPU.

Well, my preferred choice would be automatic adjustment with a module
parameter.  If we need manual tuning, per-CPU would be my choice, but
automatic is nicer anyway. :)

Paolo