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KVM: arm/arm64: Enable adaptative WFE trapping 

Trapping blocking WFE is extremely beneficial in situations where
the system is oversubscribed, as it allows another thread to run
while being blocked. In a non-oversubscribed environment, this is
the complete opposite, and trapping WFE is just unnecessary overhead.

Let's only enable WFE trapping if the CPU has more than a single task
to run (that is, more than just the vcpu thread).

Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
This commit is contained in:
Marc Zyngier 2018-06-21 10:43:59 +01:00
parent 0a72a5ab9f
commit de73708915
3 changed files with 26 additions and 0 deletions
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10
arch/arm/include/asm/kvm_emulate.h
View File

@ -107,6 +107,16 @@ static inline unsigned long *vcpu_hcr(const struct kvm_vcpu *vcpu)
return (unsigned long *)&vcpu->arch.hcr;
}
static inline void vcpu_clear_wfe_traps(struct kvm_vcpu *vcpu)
{
vcpu->arch.hcr &= ~HCR_TWE;
}
static inline void vcpu_set_wfe_traps(struct kvm_vcpu *vcpu)
{
vcpu->arch.hcr |= HCR_TWE;
}
static inline bool vcpu_mode_is_32bit(const struct kvm_vcpu *vcpu)
{
return 1;

10
arch/arm64/include/asm/kvm_emulate.h
View File

@ -83,6 +83,16 @@ static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
return (unsigned long *)&vcpu->arch.hcr_el2;
}
static inline void vcpu_clear_wfe_traps(struct kvm_vcpu *vcpu)
{
vcpu->arch.hcr_el2 &= ~HCR_TWE;
}
static inline void vcpu_set_wfe_traps(struct kvm_vcpu *vcpu)
{
vcpu->arch.hcr_el2 |= HCR_TWE;
}
static inline void vcpu_set_vsesr(struct kvm_vcpu *vcpu, u64 vsesr)
{
vcpu->arch.vsesr_el2 = vsesr;

6
virt/kvm/arm/arm.c
View File

@ -30,6 +30,7 @@
#include <linux/kvm.h>
#include <linux/kvm_irqfd.h>
#include <linux/irqbypass.h>
#include <linux/sched/stat.h>
#include <trace/events/kvm.h>
#include <kvm/arm_pmu.h>
#include <kvm/arm_psci.h>
@ -380,6 +381,11 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
kvm_timer_vcpu_load(vcpu);
kvm_vcpu_load_sysregs(vcpu);
kvm_arch_vcpu_load_fp(vcpu);
if (single_task_running())
vcpu_clear_wfe_traps(vcpu);
else
vcpu_set_wfe_traps(vcpu);
}
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)