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

A third new parameter, ple_window_max, controls a maximal ple_window.
A minimum equals to ple_window.

Signed-off-by: Radim Krčmář <rkrc...@redhat.com>
---
 arch/x86/kvm/vmx.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 78 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 18e0e52..e63d7ac 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -125,14 +125,32 @@ 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
+#define KVM_VMX_DEFAULT_PLE_WINDOW_MAX    \
+               INT_MAX / KVM_VMX_DEFAULT_PLE_WINDOW_GROW
+
 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);
+
+/* Default is to compute the maximum so we can never overflow. */
+static int ple_window_actual_max = KVM_VMX_DEFAULT_PLE_WINDOW_MAX;
+static int ple_window_max        = KVM_VMX_DEFAULT_PLE_WINDOW_MAX;
+module_param(ple_window_max, int, S_IRUGO);
+
 extern const ulong vmx_return;
 
 #define NR_AUTOLOAD_MSRS 8
@@ -5679,12 +5697,66 @@ out:
        return ret;
 }
 
+static int __grow_ple_window(int val)
+{
+       if (ple_window_grow < 1)
+               return ple_window;
+
+       val = min(val, ple_window_actual_max);
+
+       if (ple_window_grow < ple_window)
+               val *= ple_window_grow;
+       else
+               val += ple_window_grow;
+
+       return val;
+}
+
+static int __shrink_ple_window(int val, int shrinker, int minimum)
+{
+       if (shrinker < 1)
+               return ple_window;
+
+       if (shrinker < ple_window)
+               val /= shrinker;
+       else
+               val -= shrinker;
+
+       return max(val, minimum);
+}
+
+static void modify_ple_window(struct kvm_vcpu *vcpu, int grow)
+{
+       struct vcpu_vmx *vmx = to_vmx(vcpu);
+       int new;
+
+       if (grow)
+               new = __grow_ple_window(vmx->ple_window);
+       else
+               new = __shrink_ple_window(vmx->ple_window, ple_window_shrink,
+                                         ple_window);
+
+       vmx->ple_window = max(new, ple_window);
+}
+#define grow_ple_window(vcpu)   modify_ple_window(vcpu, 1)
+#define shrink_ple_window(vcpu) modify_ple_window(vcpu, 0)
+
+static void update_ple_window_actual_max(void)
+{
+       ple_window_actual_max =
+                       __shrink_ple_window(max(ple_window_max, ple_window),
+                                           ple_window_grow, INT_MIN);
+}
+
 /*
  * 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);
 
@@ -8854,6 +8926,8 @@ 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 = {
@@ -9077,6 +9151,8 @@ static int __init vmx_init(void)
        } else
                kvm_disable_tdp();
 
+       update_ple_window_actual_max();
+
        return 0;
 
 out7:
-- 
2.0.4

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Reply via email to