Commit b4a2d31d authored by Radim Krčmář's avatar Radim Krčmář Committed by Paolo Bonzini
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KVM: VMX: dynamise PLE window 



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 the maximal ple_window;
it is internally rounded down to a closest multiple of ple_window_grow.

VCPU's PLE window is never allowed below ple_window.

Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a7653ecd

arch/x86/kvm/vmx.c

+93 −2
Original line number Diff line number Diff line
@@ -127,12 +127,30 @@ module_param(nested, bool, S_IRUGO); 
 */

#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
@@ -5683,12 +5701,81 @@ 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 modifier, int minimum)

{

	if (modifier < 1)

		return ple_window;



	if (modifier < ple_window)

		val /= modifier;

	else

		val -= modifier;



	return max(val, minimum);

}



static void grow_ple_window(struct kvm_vcpu *vcpu)

{

	struct vcpu_vmx *vmx = to_vmx(vcpu);

	int old = vmx->ple_window;



	vmx->ple_window = __grow_ple_window(old);



	if (vmx->ple_window != old)

		vmx->ple_window_dirty = true;

}



static void shrink_ple_window(struct kvm_vcpu *vcpu)

{

	struct vcpu_vmx *vmx = to_vmx(vcpu);

	int old = vmx->ple_window;



	vmx->ple_window = __shrink_ple_window(old,

	                                      ple_window_shrink, ple_window);



	if (vmx->ple_window != old)

		vmx->ple_window_dirty = true;

}



/*

 * 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);

}



/*

 * 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);
@@ -8860,6 +8947,8 @@ 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 = {
@@ -9082,6 +9171,8 @@ static int __init vmx_init(void) 
	} else

		kvm_disable_tdp();



	update_ple_window_actual_max();



	return 0;



out7:

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