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

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@xxxxxx>
  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)

  #endif        /* CONFIG_PARAVIRT_SPINLOCKS */
+ * 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

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.


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