2019-07-23 23:22:16

by luferry

Subject: [PATCH] KVM: x86: init x2apic_enabled() once

From: luferry <[email protected]>

x2apic_eanbled() costs about 200 cycles
when guest trigger halt pretty high, pi ops in hotpath

Signed-off-by: luferry <[email protected]>
---
arch/x86/kvm/vmx/vmx.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d98eac371c0a..e17dbf011e47 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -186,6 +186,8 @@ static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond);
static DEFINE_MUTEX(vmx_l1d_flush_mutex);

+static int __read_mostly host_x2apic_enabled;
+
/* Storage for pre module init parameter parsing */
static enum vmx_l1d_flush_state __read_mostly vmentry_l1d_flush_param = VMENTER_L1D_FLUSH_AUTO;

@@ -1204,7 +1206,7 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)

dest = cpu_physical_id(cpu);

- if (x2apic_enabled())
+ if (host_x2apic_enabled)
new.ndst = dest;
else
new.ndst = (dest << 8) & 0xFF00;
@@ -7151,7 +7153,7 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)

dest = cpu_physical_id(vcpu->cpu);

- if (x2apic_enabled())
+ if (host_x2apic_enabled)
new.ndst = dest;
else
new.ndst = (dest << 8) & 0xFF00;
@@ -7221,7 +7223,7 @@ static int pi_pre_block(struct kvm_vcpu *vcpu)
*/
dest = cpu_physical_id(vcpu->pre_pcpu);

- if (x2apic_enabled())
+ if (host_x2apic_enabled)
new.ndst = dest;
else
new.ndst = (dest << 8) & 0xFF00;
@@ -7804,6 +7806,8 @@ static int __init vmx_init(void)
}
#endif

+ host_x2apic_enabled = x2apic_enabled();
+
r = kvm_init(&vmx_x86_ops, sizeof(struct vcpu_vmx),
__alignof__(struct vcpu_vmx), THIS_MODULE);
if (r)
--
2.14.1.40.g8e62ba1

2019-07-24 02:31:54

by Krish Sadhukhan

Subject: Re: [PATCH] KVM: x86: init x2apic_enabled() once

On 07/23/2019 06:06 AM, [email protected] wrote:
> From: luferry <[email protected]>
>
> x2apic_eanbled() costs about 200 cycles
> when guest trigger halt pretty high, pi ops in hotpath
>
> Signed-off-by: luferry <[email protected]>
> ---
> arch/x86/kvm/vmx/vmx.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index d98eac371c0a..e17dbf011e47 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -186,6 +186,8 @@ static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
> static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond);
> static DEFINE_MUTEX(vmx_l1d_flush_mutex);
>
> +static int __read_mostly host_x2apic_enabled;
> +
> /* Storage for pre module init parameter parsing */
> static enum vmx_l1d_flush_state __read_mostly vmentry_l1d_flush_param = VMENTER_L1D_FLUSH_AUTO;
>
> @@ -1204,7 +1206,7 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
>
> dest = cpu_physical_id(cpu);
>
> - if (x2apic_enabled())
> + if (host_x2apic_enabled)
> new.ndst = dest;
> else
> new.ndst = (dest << 8) & 0xFF00;
> @@ -7151,7 +7153,7 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
>
> dest = cpu_physical_id(vcpu->cpu);
>
> - if (x2apic_enabled())
> + if (host_x2apic_enabled)
> new.ndst = dest;
> else
> new.ndst = (dest << 8) & 0xFF00;
> @@ -7221,7 +7223,7 @@ static int pi_pre_block(struct kvm_vcpu *vcpu)
> */
> dest = cpu_physical_id(vcpu->pre_pcpu);
>
> - if (x2apic_enabled())
> + if (host_x2apic_enabled)
> new.ndst = dest;
> else
> new.ndst = (dest << 8) & 0xFF00;
> @@ -7804,6 +7806,8 @@ static int __init vmx_init(void)
> }
> #endif
>
> + host_x2apic_enabled = x2apic_enabled();
> +
> r = kvm_init(&vmx_x86_ops, sizeof(struct vcpu_vmx),
> __alignof__(struct vcpu_vmx), THIS_MODULE);
> if (r)

Reviewed-by: Krish Sadhukhan <[email protected]>

2019-07-24 17:41:22

by Sean Christopherson

Subject: Re: [PATCH] KVM: x86: init x2apic_enabled() once

On Tue, Jul 23, 2019 at 09:06:08PM +0800, [email protected] wrote:
> From: luferry <[email protected]>
>
> x2apic_eanbled() costs about 200 cycles
> when guest trigger halt pretty high, pi ops in hotpath
>
> Signed-off-by: luferry <[email protected]>
> ---
> arch/x86/kvm/vmx/vmx.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index d98eac371c0a..e17dbf011e47 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -186,6 +186,8 @@ static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
> static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond);
> static DEFINE_MUTEX(vmx_l1d_flush_mutex);
>
> +static int __read_mostly host_x2apic_enabled;
> +
> /* Storage for pre module init parameter parsing */
> static enum vmx_l1d_flush_state __read_mostly vmentry_l1d_flush_param = VMENTER_L1D_FLUSH_AUTO;
>
> @@ -1204,7 +1206,7 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
>
> dest = cpu_physical_id(cpu);
>
> - if (x2apic_enabled())
> + if (host_x2apic_enabled)

Instead of caching x2apic_enabled(), this can be:

if (x2apic_supported() && x2apic_mode)

which will get compiled out if CONFIG_X86_X2APIC=n.

It's quite suprising (to me) that 2apic_enabled() reads the MSR in the
first place, but at a glance the other users of x2apic_enabled() do need
to query the MSR and/or may be called before x2apic_mode is set.

> new.ndst = dest;
> else
> new.ndst = (dest << 8) & 0xFF00;
> @@ -7151,7 +7153,7 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
>
> dest = cpu_physical_id(vcpu->cpu);
>
> - if (x2apic_enabled())
> + if (host_x2apic_enabled)
> new.ndst = dest;
> else
> new.ndst = (dest << 8) & 0xFF00;
> @@ -7221,7 +7223,7 @@ static int pi_pre_block(struct kvm_vcpu *vcpu)
> */
> dest = cpu_physical_id(vcpu->pre_pcpu);
>
> - if (x2apic_enabled())
> + if (host_x2apic_enabled)
> new.ndst = dest;
> else
> new.ndst = (dest << 8) & 0xFF00;
> @@ -7804,6 +7806,8 @@ static int __init vmx_init(void)
> }
> #endif
>
> + host_x2apic_enabled = x2apic_enabled();
> +
> r = kvm_init(&vmx_x86_ops, sizeof(struct vcpu_vmx),
> __alignof__(struct vcpu_vmx), THIS_MODULE);
> if (r)
> --
> 2.14.1.40.g8e62ba1
>
>