Re: [PATCH v7 07/11] pvqspinlock, x86: Allow unfair queue spinlock in a XEN guest

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

On 03/19/2014 04:28 PM, Konrad Rzeszutek Wilk wrote:
> On Wed, Mar 19, 2014 at 04:14:05PM -0400, Waiman Long wrote:
>> This patch adds a XEN init function to activate the unfair queue
>> spinlock in a XEN guest when the PARAVIRT_UNFAIR_LOCKS kernel config
>> option is selected.
>>
>> Signed-off-by: Waiman Long<Waiman.Long@hp.com>
>> ---
>>   arch/x86/xen/setup.c |   19 +++++++++++++++++++
>>   1 files changed, 19 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
>> index 0982233..66bb6f5 100644
>> --- a/arch/x86/xen/setup.c
>> +++ b/arch/x86/xen/setup.c
>> @@ -625,3 +625,22 @@ void __init xen_arch_setup(void)
>>   	numa_off = 1;
>>   #endif
>>   }
>> +
>> +#ifdef CONFIG_PARAVIRT_UNFAIR_LOCKS
>> +/*
>> + * Enable unfair lock if running in a Xen guest
>> + */
>> +static __init int xen_unfair_locks_init_jump(void)
>> +{
>> +	/*
>> +	 * Disable unfair lock if not running in a PV domain
>> +	 */
>> +	if (!xen_pv_domain())
>> +		return 0;
> I would just make this 'xen_domain'. Not sure why you need
> to have it only for PV while the PVHVM guests can also use it?

The compilation of the setup.c file should have implied xen_domain 
already (at least HVM). The check is added to make sure that unfair lock 
won't be enabled on bare metal. As for PVHVM, is there a way to detect 
it is running as such which is distinct from HVM?

> Would it also make sense to use the same printk statement
> that the KVM has?
>

Yes, I can add a printk statement like KVM.

-Longman