Re: [PATCH RFC v5 5/8] pvqspinlock, x86: Enable unfair queue spinlock in a KVM guest

[Waiman Long <waiman.long@hp.com>]

On 02/26/2014 12:08 PM, Konrad Rzeszutek Wilk wrote:
> On Wed, Feb 26, 2014 at 10:14:25AM -0500, Waiman Long wrote:
>> This patch adds a KVM init function to activate the unfair queue
>> spinlock in a KVM guest when the PARAVIRT_UNFAIR_LOCKS kernel config
>> option is selected.
>>
>> Signed-off-by: Waiman Long<Waiman.Long@hp.com>
>> ---
>>   arch/x86/kernel/kvm.c |   17 +++++++++++++++++
>>   1 files changed, 17 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>> index 713f1b3..a489140 100644
>> --- a/arch/x86/kernel/kvm.c
>> +++ b/arch/x86/kernel/kvm.c
>> @@ -826,3 +826,20 @@ static __init int kvm_spinlock_init_jump(void)
>>   early_initcall(kvm_spinlock_init_jump);
>>
>>   #endif	/* CONFIG_PARAVIRT_SPINLOCKS */
>> +
>> +#ifdef CONFIG_PARAVIRT_UNFAIR_LOCKS
>> +/*
>> + * Enable unfair lock if running in a real para-virtualized environment
>> + */
>> +static __init int kvm_unfair_locks_init_jump(void)
>> +{
>> +	if (!kvm_para_available())
>> +		return 0;
> I think you also need to check for !kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)?
> Otherwise you might enable this, but the kicker function won't be
> enabled.

The unfair lock code doesn't need to use the CPU kicker function. That 
is why the KVM_FEATURE_PV_UNHALT feature is not checked.

-Longman