linux-kernel - Re: [PATCH 1/1] kvm : vmx : Remove yield_on

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Date:	Tue, 07 Feb 2012 12:04:14 -0600
From:	Anthony Liguori <aliguori@...ibm.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	KVM <kvm@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marcelo Tosatti <mtosatti@...hat.com>, X86 <x86@...nel.org>,
	Ingo Molnar <mingo@...hat.com>, Avi Kivity <avi@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH 1/1] kvm : vmx : Remove yield_on_hlt

On 02/07/2012 11:49 AM, Raghavendra K T wrote:
>    yield_on_hlt was introduced for CPU bandwidth capping. now it is redundant
> with CFS hardlimit.
>
> yield_on_hlt also complicates the scenario in paravirtual environment, that
> needs to trap halt. for e.g. paravirtualized ticket spinlocks.
>
> Changelog:
> Remove the support for yield_on_hlt.
>
> Signed-off-by: Raghavendra K T<raghavendra.kt@...ux.vnet.ibm.com>

Acked-by: Anthony Liguori <aliguori@...ibm.com>

Regards,

Anthony Liguori

> ---
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index d29216c..2fb3009 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -70,9 +70,6 @@ module_param(emulate_invalid_guest_state, bool, S_IRUGO);
>   static bool __read_mostly vmm_exclusive = 1;
>   module_param(vmm_exclusive, bool, S_IRUGO);
>
> -static bool __read_mostly yield_on_hlt = 1;
> -module_param(yield_on_hlt, bool, S_IRUGO);
> -
>   static bool __read_mostly fasteoi = 1;
>   module_param(fasteoi, bool, S_IRUGO);
>
> @@ -1655,17 +1652,6 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
>   	vmx_set_interrupt_shadow(vcpu, 0);
>   }
>
> -static void vmx_clear_hlt(struct kvm_vcpu *vcpu)
> -{
> -	/* Ensure that we clear the HLT state in the VMCS.  We don't need to
> -	 * explicitly skip the instruction because if the HLT state is set, then
> -	 * the instruction is already executing and RIP has already been
> -	 * advanced. */
> -	if (!yield_on_hlt&&
> -	    vmcs_read32(GUEST_ACTIVITY_STATE) == GUEST_ACTIVITY_HLT)
> -		vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
> -}
> -
>   /*
>    * KVM wants to inject page-faults which it got to the guest. This function
>    * checks whether in a nested guest, we need to inject them to L1 or L2.
> @@ -1718,7 +1704,6 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
>   		intr_info |= INTR_TYPE_HARD_EXCEPTION;
>
>   	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
> -	vmx_clear_hlt(vcpu);
>   }
>
>   static bool vmx_rdtscp_supported(void)
> @@ -2399,7 +2384,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
>   				&_pin_based_exec_control)<  0)
>   		return -EIO;
>
> -	min =
> +	min = CPU_BASED_HLT_EXITING |
>   #ifdef CONFIG_X86_64
>   	      CPU_BASED_CR8_LOAD_EXITING |
>   	      CPU_BASED_CR8_STORE_EXITING |
> @@ -2414,9 +2399,6 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
>   	      CPU_BASED_INVLPG_EXITING |
>   	      CPU_BASED_RDPMC_EXITING;
>
> -	if (yield_on_hlt)
> -		min |= CPU_BASED_HLT_EXITING;
> -
>   	opt = CPU_BASED_TPR_SHADOW |
>   	      CPU_BASED_USE_MSR_BITMAPS |
>   	      CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
> @@ -4003,7 +3985,6 @@ static void vmx_inject_irq(struct kvm_vcpu *vcpu)
>   	} else
>   		intr |= INTR_TYPE_EXT_INTR;
>   	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr);
> -	vmx_clear_hlt(vcpu);
>   }
>
>   static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
> @@ -4035,7 +4016,6 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
>   	}
>   	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
>   			INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK | NMI_VECTOR);
> -	vmx_clear_hlt(vcpu);
>   }
>
>   static int vmx_nmi_allowed(struct kvm_vcpu *vcpu)

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