[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

On 02/27/2014 05:40 AM, Raghavendra K T wrote:
On 02/26/2014 08:44 PM, 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)

+ * 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;

kvm_kick_cpu_type() in patch 8 assumes that host has support for kick
hypercall (KVM_HC_KICK_CPU).

I think for that we need explicit check of this kvm_para_has_feature(KVM_FEATURE_PV_UNHALT).

otherwise things may break for unlikely case of running a new guest on
a old host?

Unfair lock is a separate config option that does not need to do any cpu kick. The checking of kvm_para_available() is just to make sure that the kernel is running in a real PV environment, not on bare metal but with CONFIG_PARAVIRT enabled.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.