Window is increased on every PLE exit and decreased on every sched_in.
The idea is that we don't want to PLE exit if there is no preemption
going on.
We do this with sched_in() because it does not hold rq lock.
There are two new kernel parameters for changing the window:
ple_window_grow and ple_window_shrink
ple_window_grow affects the window on PLE exit and ple_window_shrink
does it on sched_in; depending on their value, the window is modifier
like this: (ple_window is kvm_intel's global)
ple_window_shrink/ |
ple_window_grow | PLE exit | sched_in
-------------------+--------------------+---------------------
< 1 | = ple_window | = ple_window
< ple_window | *= ple_window_grow | /= ple_window_shrink
otherwise | += ple_window_grow | -= ple_window_shrink
Signed-off-by: Radim Krčmář <rkrc...@redhat.com>
---
arch/x86/kvm/vmx.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 50 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index eaa5574..66259fd 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -125,14 +125,25 @@ module_param(nested, bool, S_IRUGO);
* Time is measured based on a counter that runs at the same rate as the TSC,
* refer SDM volume 3b section 21.6.13 & 22.1.3.
*/
-#define KVM_VMX_DEFAULT_PLE_GAP 128
-#define KVM_VMX_DEFAULT_PLE_WINDOW 4096
+#define KVM_VMX_DEFAULT_PLE_GAP 128
+#define KVM_VMX_DEFAULT_PLE_WINDOW 4096
+#define KVM_VMX_DEFAULT_PLE_WINDOW_GROW 2
+#define KVM_VMX_DEFAULT_PLE_WINDOW_SHRINK 0
+
static int ple_gap = KVM_VMX_DEFAULT_PLE_GAP;
module_param(ple_gap, int, S_IRUGO);
static int ple_window = KVM_VMX_DEFAULT_PLE_WINDOW;
module_param(ple_window, int, S_IRUGO);
+/* Default doubles per-vcpu window every exit. */
+static int ple_window_grow = KVM_VMX_DEFAULT_PLE_WINDOW_GROW;
+module_param(ple_window_grow, int, S_IRUGO);
+
+/* Default resets per-vcpu window every exit to ple_window. */
+static int ple_window_shrink = KVM_VMX_DEFAULT_PLE_WINDOW_SHRINK;
+module_param(ple_window_shrink, int, S_IRUGO);
+
extern const ulong vmx_return;
#define NR_AUTOLOAD_MSRS 8
@@ -5680,12 +5691,47 @@ out:
return ret;
}
+static void grow_ple_window(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+ int old = vmx->ple_window;
+ int new;
+
+ if (ple_window_grow < 1)
+ new = ple_window;
+ else if (ple_window_grow < ple_window)
+ new = old * ple_window_grow;
+ else
+ new = old + ple_window_grow;
+
+ vmx->ple_window = new;
+}
+
+static void shrink_ple_window(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+ int old = vmx->ple_window;
+ int new;
+
+ if (ple_window_shrink < 1)
+ new = ple_window;
+ else if (ple_window_shrink < ple_window)
+ new = old / ple_window_shrink;
+ else
+ new = old - ple_window_shrink;
+
+ vmx->ple_window = new;
+}
+
/*
* Indicate a busy-waiting vcpu in spinlock. We do not enable the PAUSE
* exiting, so only get here on cpu with PAUSE-Loop-Exiting.
*/
static int handle_pause(struct kvm_vcpu *vcpu)
{
+ if (ple_gap)
+ grow_ple_window(vcpu);
+
skip_emulated_instruction(vcpu);
kvm_vcpu_on_spin(vcpu);
@@ -8855,6 +8901,8 @@ static int vmx_check_intercept(struct kvm_vcpu *vcpu,
void vmx_sched_in(struct kvm_vcpu *vcpu, int cpu)
{
+ if (ple_gap)
+ shrink_ple_window(vcpu);
}
static struct kvm_x86_ops vmx_x86_ops = {
--
2.0.4
--
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