Re: [PATCH v2 4/6] KVM: VMX: dynamise PLE window

[Paolo Bonzini <pbonzini@redhat.com>]

Il 20/08/2014 22:53, Radim Krčmář ha scritto:
> 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 <rkrcmar@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)

s/shrinker/factor/ or s/shrinker/param/ (shrinker has another meaning in
the kernel).

> +{
> +	if (shrinker < 1)
> +		return ple_window;
> +
> +	if (shrinker < ple_window)
> +		val /= shrinker;
> +	else
> +		val -= shrinker;
> +
> +	return max(val, minimum);

Any reason to use anything but ple_window as the minimum, even in
update_ple_window_actual_max?

> +}
> +
> +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)

No macros please. :)

Paolo

> +
> +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:
>