[v2,2/5] KVM: VMX: Remove ple_window_actual_max

Commit Message

Babu Moger March 16, 2018, 8:37 p.m. UTC

Get rid of ple_window_actual_max, because its benefits are really
minuscule and the logic is complicated.

The overflows(and underflow) are controlled in __ple_window_grow
and _ple_window_shrink respectively.

Suggested-by: Radim Krčmář <[e-mail]>
Signed-off-by: Babu Moger <[e-mail]>
---
 arch/x86/kvm/vmx.c | 22 +---------------------
 1 file changed, 1 insertion(+), 21 deletions(-)

Comments

Radim Krčmář March 28, 2018, 8:24 p.m. UTC | #1

2018-03-16 16:37-0400, Babu Moger:
> Get rid of ple_window_actual_max, because its benefits are really
> minuscule and the logic is complicated.
> 
> The overflows(and underflow) are controlled in __ple_window_grow
> and _ple_window_shrink respectively.
> 
> Suggested-by: Radim Krčmář <[e-mail]>
> Signed-off-by: Babu Moger <[e-mail]>
> ---
>  arch/x86/kvm/vmx.c | 22 +---------------------
>  1 file changed, 1 insertion(+), 21 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> @@ -178,7 +178,6 @@
>  module_param(ple_window_shrink, uint, 0444);
>  
>  /* Default is to compute the maximum so we can never overflow. */
> -static uint ple_window_actual_max = KVM_VMX_DEFAULT_PLE_WINDOW_MAX;
>  static uint ple_window_max        = KVM_VMX_DEFAULT_PLE_WINDOW_MAX;
>  module_param(ple_window_max, uint, 0444);
>  
> @@ -6645,14 +6644,12 @@ static uint __grow_ple_window(uint 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;
> +	return min(val, ple_window_max);

I added a bit of logic to avoid wraparounds.

Patch

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c9a9080..b992d81 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -178,7 +178,6 @@ 
 module_param(ple_window_shrink, uint, 0444);
 
 /* Default is to compute the maximum so we can never overflow. */
-static uint ple_window_actual_max = KVM_VMX_DEFAULT_PLE_WINDOW_MAX;
 static uint ple_window_max        = KVM_VMX_DEFAULT_PLE_WINDOW_MAX;
 module_param(ple_window_max, uint, 0444);
 
@@ -6645,14 +6644,12 @@  static uint __grow_ple_window(uint 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;
+	return min(val, ple_window_max);
 }
 
 static uint __shrink_ple_window(uint val, uint modifier, uint minimum)
@@ -6696,21 +6693,6 @@  static void shrink_ple_window(struct kvm_vcpu *vcpu)
 }
 
 /*
- * ple_window_actual_max is computed to be one grow_ple_window() below
- * ple_window_max. (See __grow_ple_window for the reason.)
- * This prevents overflows, because ple_window_max is int.
- * ple_window_max effectively rounded down to a multiple of ple_window_grow in
- * this process.
- * ple_window_max is also prevented from setting vmx->ple_window < ple_window.
- */
-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);
-}
-
-/*
  * Handler for POSTED_INTERRUPT_WAKEUP_VECTOR.
  */
 static void wakeup_handler(void)
@@ -6876,8 +6858,6 @@  static __init int hardware_setup(void)
 	else
 		kvm_disable_tdp();
 
-	update_ple_window_actual_max();
-
 	/*
 	 * Only enable PML when hardware supports PML feature, and both EPT
 	 * and EPT A/D bit features are enabled -- PML depends on them to work.