From b4a2d31da812ce03efaf5d30c6b9d39c1cbd18d8 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Date: Thu, 21 Aug 2014 18:08:08 +0200 Subject: [PATCH] KVM: VMX: dynamise PLE window MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx.c | 95 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 93 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 70175990536b..baeac7f580a7 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 @@ -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: -- 2.39.2