From b080935c8638e08134629d0a9ebdf35669bec14d Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 5 Oct 2012 23:07:19 +0200 Subject: [PATCH] kvm: Directly account vtime to system on guest switch Switching to or from guest context is done on ioctl context. So by the time we call kvm_guest_enter() or kvm_guest_exit() we know we are not running the idle task. As a result, we can directly account the cputime using vtime_account_system(). There are two good reasons to do this: * We avoid some useless checks on guest switch. It optimizes a bit this fast path. * In the case of CONFIG_IRQ_TIME_ACCOUNTING, calling vtime_account() checks for irq time to account. This is pointless since we know we are not in an irq on guest switch. This is wasting cpu cycles for no good reason. vtime_account_system() OTOH is a no-op in this config option. * We can remove the irq disable/enable around kvm guest switch in s390. A further optimization may consist in introducing a vtime_account_guest() that directly calls account_guest_time(). Signed-off-by: Frederic Weisbecker Cc: Tony Luck Cc: Fenghua Yu Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Heiko Carstens Cc: Martin Schwidefsky Cc: Avi Kivity Cc: Marcelo Tosatti Cc: Joerg Roedel Cc: Alexander Graf Cc: Xiantao Zhang Cc: Christian Borntraeger Cc: Cornelia Huck Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Steven Rostedt Cc: Paul Gortmaker --- arch/s390/kvm/kvm-s390.c | 4 ---- include/linux/kvm_host.h | 12 ++++++++++-- 2 files changed, 10 insertions(+), 6 deletions(-) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index ecced9d18986..d91a95568002 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -608,9 +608,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu) kvm_s390_deliver_pending_interrupts(vcpu); vcpu->arch.sie_block->icptcode = 0; - local_irq_disable(); kvm_guest_enter(); - local_irq_enable(); VCPU_EVENT(vcpu, 6, "entering sie flags %x", atomic_read(&vcpu->arch.sie_block->cpuflags)); trace_kvm_s390_sie_enter(vcpu, @@ -629,9 +627,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu) VCPU_EVENT(vcpu, 6, "exit sie icptcode %d", vcpu->arch.sie_block->icptcode); trace_kvm_s390_sie_exit(vcpu, vcpu->arch.sie_block->icptcode); - local_irq_disable(); kvm_guest_exit(); - local_irq_enable(); memcpy(&vcpu->run->s.regs.gprs[14], &vcpu->arch.sie_block->gg14, 16); return rc; diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 93bfc9f9815c..0e2212fe4784 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -737,7 +737,11 @@ static inline int kvm_deassign_device(struct kvm *kvm, static inline void kvm_guest_enter(void) { BUG_ON(preemptible()); - vtime_account(current); + /* + * This is running in ioctl context so we can avoid + * the call to vtime_account() with its unnecessary idle check. + */ + vtime_account_system(current); current->flags |= PF_VCPU; /* KVM does not hold any references to rcu protected data when it * switches CPU into a guest mode. In fact switching to a guest mode @@ -751,7 +755,11 @@ static inline void kvm_guest_enter(void) static inline void kvm_guest_exit(void) { - vtime_account(current); + /* + * This is running in ioctl context so we can avoid + * the call to vtime_account() with its unnecessary idle check. + */ + vtime_account_system(current); current->flags &= ~PF_VCPU; }