On 07/10/13 16:52, Bhushan Bharat-R65777 wrote: > > >> -----Original Message----- >> From: Marc Zyngier [mailto:marc.zyngier@xxxxxxx] >> Sent: Monday, October 07, 2013 9:11 PM >> To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx; >> kvm@xxxxxxxxxxxxxxx >> Subject: [PATCH 2/2] arm64: KVM: Yield CPU when vcpu executes a WFE >> >> On an (even slightly) oversubscribed system, spinlocks are quickly becoming a >> bottleneck, as some vcpus are spinning, waiting for a lock to be released, while >> the vcpu holding the lock may not be running at all. >> >> The solution is to trap blocking WFEs and tell KVM that we're now spinning. This >> ensures that other vpus will get a scheduling boost, allowing the lock to be >> released more quickly. >> >> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> >> --- >> arch/arm64/include/asm/kvm_arm.h | 8 ++++++-- >> arch/arm64/kvm/handle_exit.c | 18 +++++++++++++----- >> 2 files changed, 19 insertions(+), 7 deletions(-) >> >> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h >> index a5f28e2..c98ef47 100644 >> --- a/arch/arm64/include/asm/kvm_arm.h >> +++ b/arch/arm64/include/asm/kvm_arm.h >> @@ -63,6 +63,7 @@ >> * TAC: Trap ACTLR >> * TSC: Trap SMC >> * TSW: Trap cache operations by set/way >> + * TWE: Trap WFE >> * TWI: Trap WFI >> * TIDCP: Trap L2CTLR/L2ECTLR >> * BSU_IS: Upgrade barriers to the inner shareable domain >> @@ -72,8 +73,9 @@ >> * FMO: Override CPSR.F and enable signaling with VF >> * SWIO: Turn set/way invalidates into set/way clean+invalidate >> */ >> -#define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWI | HCR_VM | HCR_BSU_IS | \ >> - HCR_FB | HCR_TAC | HCR_AMO | HCR_IMO | HCR_FMO | \ >> +#define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWE | HCR_TWI | HCR_VM | \ >> + HCR_BSU_IS | HCR_FB | HCR_TAC | \ >> + HCR_AMO | HCR_IMO | HCR_FMO | \ >> HCR_SWIO | HCR_TIDCP | HCR_RW) >> #define HCR_VIRT_EXCP_MASK (HCR_VA | HCR_VI | HCR_VF) >> >> @@ -242,4 +244,6 @@ >> >> #define ESR_EL2_EC_xABT_xFSR_EXTABT 0x10 >> >> +#define ESR_EL2_EC_WFI_ISS_WFE (1 << 0) > > In another patch this is named as WHI_IS_WFE whereas here it is WFI_ISS_WFE, looks like typo. Anyways, what I am interested to understand is what does this macro means? Not a typo. It decodes as: Exception Status Register, Exception Level 2, Exception Class Wait For Interrupt, Instruction Specific Syndrome Wait For Event. The ARM code doesn't have such a convention, so I didn't bother. It just reads "Hyp Status Register, Wait For Interrupt Is Wait For Event". M. > Thanks > -Bharat > >> + >> #endif /* __ARM64_KVM_ARM_H__ */ >> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c index >> 9beaca03..8da5606 100644 >> --- a/arch/arm64/kvm/handle_exit.c >> +++ b/arch/arm64/kvm/handle_exit.c >> @@ -47,21 +47,29 @@ static int handle_smc(struct kvm_vcpu *vcpu, struct kvm_run >> *run) } >> >> /** >> - * kvm_handle_wfi - handle a wait-for-interrupts instruction executed by a >> guest >> + * kvm_handle_wfx - handle a wait-for-interrupts or wait-for-event >> + * instruction executed by a guest >> + * >> * @vcpu: the vcpu pointer >> * >> - * Simply call kvm_vcpu_block(), which will halt execution of >> + * WFE: Yield the CPU and come back to this vcpu when the scheduler >> + * decides to. >> + * WFI: Simply call kvm_vcpu_block(), which will halt execution of >> * world-switches and schedule other host processes until there is an >> * incoming IRQ or FIQ to the VM. >> */ >> -static int kvm_handle_wfi(struct kvm_vcpu *vcpu, struct kvm_run *run) >> +static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run) >> { >> - kvm_vcpu_block(vcpu); >> + if (kvm_vcpu_get_hsr(vcpu) & ESR_EL2_EC_WFI_ISS_WFE) >> + kvm_vcpu_on_spin(vcpu); >> + else >> + kvm_vcpu_block(vcpu); >> + >> return 1; >> } >> >> static exit_handle_fn arm_exit_handlers[] = { >> - [ESR_EL2_EC_WFI] = kvm_handle_wfi, >> + [ESR_EL2_EC_WFI] = kvm_handle_wfx, >> [ESR_EL2_EC_CP15_32] = kvm_handle_cp15_32, >> [ESR_EL2_EC_CP15_64] = kvm_handle_cp15_64, >> [ESR_EL2_EC_CP14_MR] = kvm_handle_cp14_access, >> -- >> 1.8.2.3 >> >> >> >> _______________________________________________ >> kvmarm mailing list >> kvmarm@xxxxxxxxxxxxxxxxxxxxx >> https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm > > > -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
