linux-kernel - Re: [PATCH RFC 2/4] Add yield hypercall for KVM guests

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Date:	Mon, 26 Jul 2010 10:19:41 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	vatsa@...ux.vnet.ibm.com
CC:	avi@...hat.com, Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...hat.com>, linux-kernel@...r.kernel.org,
	npiggin@...e.de, kvm@...r.kernel.org, bharata@...ibm.com,
	Balbir Singh <balbir@...ibm.com>,
	Jan Beulich <JBeulich@...ell.com>
Subject: Re: [PATCH RFC 2/4] Add yield hypercall for KVM guests

  On 07/25/2010 11:14 PM, Srivatsa Vaddagiri wrote:
> Add KVM hypercall for yielding vcpu timeslice.

Can you do a directed yield?

     J

> Signed-off-by: Srivatsa Vaddagiri<vatsa@...ux.vnet.ibm.com>
>
> ---
>   arch/x86/include/asm/kvm_para.h |    1 +
>   arch/x86/kvm/x86.c              |    7 ++++++-
>   include/linux/kvm.h             |    1 +
>   include/linux/kvm_para.h        |    1 +
>   4 files changed, 9 insertions(+), 1 deletion(-)
>
> Index: current/arch/x86/include/asm/kvm_para.h
> ===================================================================
> --- current.orig/arch/x86/include/asm/kvm_para.h
> +++ current/arch/x86/include/asm/kvm_para.h
> @@ -16,6 +16,7 @@
>   #define KVM_FEATURE_CLOCKSOURCE		0
>   #define KVM_FEATURE_NOP_IO_DELAY	1
>   #define KVM_FEATURE_MMU_OP		2
> +#define KVM_FEATURE_YIELD		4
>   /* This indicates that the new set of kvmclock msrs
>    * are available. The use of 0x11 and 0x12 is deprecated
>    */
> Index: current/arch/x86/kvm/x86.c
> ===================================================================
> --- current.orig/arch/x86/kvm/x86.c
> +++ current/arch/x86/kvm/x86.c
> @@ -1618,6 +1618,7 @@ int kvm_dev_ioctl_check_extension(long e
>   	case KVM_CAP_PCI_SEGMENT:
>   	case KVM_CAP_DEBUGREGS:
>   	case KVM_CAP_X86_ROBUST_SINGLESTEP:
> +	case KVM_CAP_YIELD_HYPERCALL:
>   		r = 1;
>   		break;
>   	case KVM_CAP_COALESCED_MMIO:
> @@ -1993,7 +1994,8 @@ static void do_cpuid_ent(struct kvm_cpui
>   		entry->eax = (1<<  KVM_FEATURE_CLOCKSOURCE) |
>   			     (1<<  KVM_FEATURE_NOP_IO_DELAY) |
>   			     (1<<  KVM_FEATURE_CLOCKSOURCE2) |
> -			     (1<<  KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
> +			     (1<<  KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
> +			     (1<<  KVM_FEATURE_YIELD);
>   		entry->ebx = 0;
>   		entry->ecx = 0;
>   		entry->edx = 0;
> @@ -4245,6 +4247,9 @@ int kvm_emulate_hypercall(struct kvm_vcp
>   	case KVM_HC_MMU_OP:
>   		r = kvm_pv_mmu_op(vcpu, a0, hc_gpa(vcpu, a1, a2),&ret);
>   		break;
> +	case KVM_HC_YIELD:
> +		ret = 0;
> +		yield();
>   	default:
>   		ret = -KVM_ENOSYS;
>   		break;
> Index: current/include/linux/kvm.h
> ===================================================================
> --- current.orig/include/linux/kvm.h
> +++ current/include/linux/kvm.h
> @@ -524,6 +524,7 @@ struct kvm_enable_cap {
>   #define KVM_CAP_PPC_OSI 52
>   #define KVM_CAP_PPC_UNSET_IRQ 53
>   #define KVM_CAP_ENABLE_CAP 54
> +#define KVM_CAP_YIELD_HYPERCALL	55
>
>   #ifdef KVM_CAP_IRQ_ROUTING
>
> Index: current/include/linux/kvm_para.h
> ===================================================================
> --- current.orig/include/linux/kvm_para.h
> +++ current/include/linux/kvm_para.h
> @@ -17,6 +17,7 @@
>
>   #define KVM_HC_VAPIC_POLL_IRQ		1
>   #define KVM_HC_MMU_OP			2
> +#define KVM_HC_YIELD                    3
>
>   /*
>    * hypercalls use architecture specific
>

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