Re: [PATCH RFC V4 0/5] kvm : Paravirt-spinlock support for KVM guests

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On 16.01.2012, at 19:38, Raghavendra K T wrote:

> On 01/16/2012 07:53 PM, Alexander Graf wrote:
>> 
>> On 16.01.2012, at 15:20, Srivatsa Vaddagiri wrote:
>> 
>>> * Alexander Graf<agraf@xxxxxxx>  [2012-01-16 04:57:45]:
>>> 
>>>> Speaking of which - have you benchmarked performance degradation of pv ticket locks on bare metal?
>>> 
>>> You mean, run kernel on bare metal with CONFIG_PARAVIRT_SPINLOCKS
>>> enabled and compare how it performs with CONFIG_PARAVIRT_SPINLOCKS disabled for
>>> some workload(s)?
>> 
>> Yup
>> 
>>> 
>>> In some sense, the 1x overcommitcase results posted does measure the overhead
>>> of (pv-)spinlocks no? We don't see any overhead in that case for atleast
>>> kernbench ..
>>> 
>>>> Result for Non PLE machine :
>>>> ============================
>>> 
>>> [snip]
>>> 
>>>> Kernbench:
>>>>               BASE                    BASE+patch
>> 
>> What is BASE really? Is BASE already with the PV spinlocks enabled? I'm having a hard time understanding which tree you're working against, since the prerequisites aren't upstream yet.
>> 
>> 
>> Alex
> 
> Sorry for confusion, I think I was little imprecise on the BASE.
> 
> The BASE is pre 3.2.0 + Jeremy's following patches:
> xadd (https://lkml.org/lkml/2011/10/4/328)
> x86/ticketlocklock  (https://lkml.org/lkml/2011/10/12/496).
> So this would have ticketlock cleanups from Jeremy and
> CONFIG_PARAVIRT_SPINLOCKS=y
> 
> BASE+patch = pre 3.2.0 + Jeremy's above patches + above V5 PV spinlock
> series and CONFIG_PARAVIRT_SPINLOCKS=y
> 
> In both the cases  CONFIG_PARAVIRT_SPINLOCKS=y.
> 
> So let,
> A. pre-3.2.0 with CONFIG_PARAVIRT_SPINLOCKS = n
> B. pre-3.2.0 + Jeremy's above patches with CONFIG_PARAVIRT_SPINLOCKS = n
> C. pre-3.2.0 + Jeremy's above patches with CONFIG_PARAVIRT_SPINLOCKS = y
> D. pre-3.2.0 + Jeremy's above patches + V5 patches with CONFIG_PARAVIRT_SPINLOCKS = n
> E. pre-3.2.0 + Jeremy's above patches + V5 patches with CONFIG_PARAVIRT_SPINLOCKS = y
> 
> is it performance of A vs E ? (currently C vs E)

Since D and E only matter with KVM in use, yes, I'm mostly interested in A, B and C :).


Alex

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