From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: [PATCH/RFC 2/3] s390/kvm: Platform specific kvm_arch_vcpu_dont_yield Date: Tue, 11 Feb 2014 12:45:31 +0100 Message-ID: <1392119132-50182-3-git-send-email-borntraeger@de.ibm.com> References: <1392119132-50182-1-git-send-email-borntraeger@de.ibm.com> Return-path: In-Reply-To: <1392119132-50182-1-git-send-email-borntraeger@de.ibm.com> Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: Gleb Natapov , Paolo Bonzini Cc: KVM , linux-s390 , Cornelia Huck , Michael Mueller , Christian Borntraeger List-ID: From: Michael Mueller Commit "s390/kvm: Use common waitqueue" caused a performance regression on s390. It turned out that a yield candidate was missed by just a simple test on its non-empty waitqueue. If an interrupt is outstanding, the candidate might be suitable. kvm_arch_vcpu_dont_yield is extended by a test that additionally tests for not yet delivered interrupts. Significant performance measurement work and code analysis to solve this issue was provided by Mao Chuan Li and his team in Beijing. Signed-off-by: Michael Mueller Reviewed-by: Christian Borntraeger Signed-off-by: Christian Borntraeger --- arch/s390/kvm/Kconfig | 1 + arch/s390/kvm/kvm-s390.c | 7 +++++++ 2 files changed, 8 insertions(+) diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig index c8bacbc..e44adef 100644 --- a/arch/s390/kvm/Kconfig +++ b/arch/s390/kvm/Kconfig @@ -25,6 +25,7 @@ config KVM select HAVE_KVM_EVENTFD select KVM_ASYNC_PF select KVM_ASYNC_PF_SYNC + select HAVE_KVM_ARCH_VCPU_DONT_YIELD ---help--- Support hosting paravirtualized guest machines using the SIE virtualization capability on the mainframe. This should work diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index a5da2cc..1a33e1e 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -1231,6 +1231,13 @@ int kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf) return VM_FAULT_SIGBUS; } +#ifdef CONFIG_HAVE_KVM_ARCH_VCPU_DONT_YIELD +bool kvm_arch_vcpu_dont_yield(struct kvm_vcpu *vcpu) +{ + return waitqueue_active(&vcpu->wq) && !kvm_cpu_has_interrupt(vcpu); +} +#endif + void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *free, struct kvm_memory_slot *dont) { -- 1.8.4.2