Linux Virtualization - Mar 2014 - [PATCH RFC v6 10/11] pvqspinlock, x86: Enable qspinlock PV support for KVM

Il 13/03/2014 20:13, Waiman Long ha scritto:
>>>
>>
>> This should also disable the unfair path.
>>
>> Paolo
>>
>
> The unfair lock uses a different jump label and does not require any
> special PV ops. There is a separate init function for that.
Yeah, what I mean is that the patches that enable paravirtualization 
should also take care of decreasing the unfair-lock jump label when 
paravirtualization is enabled.

Paolo

On 03/14/2014 04:42 AM, Paolo Bonzini wrote:
> Il 13/03/2014 20:13, Waiman Long ha scritto:
>>>>
>>>
>>> This should also disable the unfair path.
>>>
>>> Paolo
>>>
>>
>> The unfair lock uses a different jump label and does not require any
>> special PV ops. There is a separate init function for that.
>
> Yeah, what I mean is that the patches that enable paravirtualization 
> should also take care of decreasing the unfair-lock jump label when 
> paravirtualization is enabled.
>
> Paolo
As there are people who don't like unfair lock at all, I prefer to give 
them the option to turn this on or off instead of forcing them to always 
use unfair lock in a PV guest.

-Longman

Il 17/03/2014 18:47, Waiman Long ha scritto:
>> Yeah, what I mean is that the patches that enable paravirtualization
>> should also take care of decreasing the unfair-lock jump label when
>> paravirtualization is enabled.
>
> As there are people who don't like unfair lock at all, I prefer to give
> them the option to turn this on or off instead of forcing them to always
> use unfair lock in a PV guest.
I understand, but this is virtualization after all.  A bad scheduler 
decision means no progress at all.  That's much worse than unfairness.

And also, KVM and Xen will stay fair, so if you want fairness just pick 
a hypervisor that supports it.

Paolo