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KVM: VMX: dynamise PLE window

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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: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Radim Krčmář 2014-08-21 18:08:08 +02:00 committed by Paolo Bonzini
parent a7653ecdf3
commit b4a2d31da8
1 changed files with 93 additions and 2 deletions
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95
arch/x86/kvm/vmx.c
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@ -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
@ -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: