From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 5/8] KVM: use jump label to optimize checking for HW enabled APIC in APIC_BASE MSR. Date: Sun, 05 Aug 2012 17:48:42 +0300 Message-ID: <501E87CA.8020302@redhat.com> References: <1344171513-4659-1-git-send-email-gleb@redhat.com> <1344171513-4659-6-git-send-email-gleb@redhat.com> <501E84A9.8040803@redhat.com> <20120805144223.GP27579@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, mtosatti@redhat.com To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:26740 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754459Ab2HEOsp (ORCPT ); Sun, 5 Aug 2012 10:48:45 -0400 Received: from int-mx12.intmail.prod.int.phx2.redhat.com (int-mx12.intmail.prod.int.phx2.redhat.com [10.5.11.25]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q75Emjeb013471 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Sun, 5 Aug 2012 10:48:45 -0400 In-Reply-To: <20120805144223.GP27579@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 08/05/2012 05:42 PM, Gleb Natapov wrote: > On Sun, Aug 05, 2012 at 05:35:21PM +0300, Avi Kivity wrote: >> On 08/05/2012 03:58 PM, Gleb Natapov wrote: >> > Usually all APICs are HW enabled so the check can be optimized out. >> > >> > Signed-off-by: Gleb Natapov >> > --- >> > arch/x86/kvm/lapic.c | 29 ++++++++++++++++++++++++++++- >> > arch/x86/kvm/lapic.h | 1 + >> > arch/x86/kvm/x86.c | 1 + >> > 3 files changed, 30 insertions(+), 1 deletion(-) >> > >> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c >> > index c3f14fe..1aa5528 100644 >> > --- a/arch/x86/kvm/lapic.c >> > +++ b/arch/x86/kvm/lapic.c >> > @@ -34,6 +34,7 @@ >> > #include >> > #include >> > #include >> > +#include >> > #include "kvm_cache_regs.h" >> > #include "irq.h" >> > #include "trace.h" >> > @@ -117,9 +118,13 @@ static inline int __apic_test_and_clear_vector(int vec, void *bitmap) >> > return __test_and_clear_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); >> > } >> > >> > +struct static_key_deferred apic_hw_disabled __read_mostly; >> >> On top of file please. Add all_ to the name to make it clear we're >> talking about all apics. >> > This is count of disabled apics really. So I think all_apic_hw_disabled > is misleading. > >> > + >> > static inline int apic_hw_enabled(struct kvm_lapic *apic) >> > { >> > - return (apic)->vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE; >> > + if (static_key_false(&apic_hw_disabled.key)) >> > + return apic->vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE; >> >> Hm, for the test to be readable, it needs to be >> >> if (static_key_false(&all_apics_hw_enabled)) >> > Exactly. all_ makes it so because apic_hw_disabled is a counter that > counts disabled apics. So may be call it global_hw_disabled_apic_counter? > The problem is how static_key_false() is defined. It returns true if the count > 0, opposite from what I'd expect. So anything with counter semantics will be confusing. I guess we need to pick a neutral name (apic_disabled_key or apic_disabled_slowpath or such) to force the reader to look at the definitions. -- error compiling committee.c: too many arguments to function