Linux Virtualization - Mar 2014 - [PATCH v7 07/11] pvqspinlock, x86: Allow unfair queue spinlock in a XEN guest

On Mar 20, 2014 11:40 PM, Waiman Long <waiman.long at hp.com>
wrote:
>
> 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 at 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?
Xen_domain() should cover PVHVM and PV.
>
> > 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