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Message-ID: <53F5AD3E.3050800@redhat.com>
Date: Thu, 21 Aug 2014 10:26:38 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Radim Krčmář <rkrcmar@...hat.com>,
kvm@...r.kernel.org
CC: linux-kernel@...r.kernel.org, Gleb Natapov <gleb@...nel.org>,
Raghavendra KT <raghavendra.kt@...ux.vnet.ibm.com>,
Vinod Chegu <chegu_vinod@...com>,
Hui-Zhi <hui-zhi.zhao@...com>,
Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH v2 4/6] KVM: VMX: dynamise PLE window
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@...hat.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:
>
--
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