From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH 16/17] TSC reset compensation Date: Wed, 16 Jun 2010 10:52:11 -0300 Message-ID: <20100616135211.GL19104@mothafucka.localdomain> References: <1276587259-32319-1-git-send-email-zamsden@redhat.com> <1276587259-32319-17-git-send-email-zamsden@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: avi@redhat.com, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Zachary Amsden Return-path: Content-Disposition: inline In-Reply-To: <1276587259-32319-17-git-send-email-zamsden@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, Jun 14, 2010 at 09:34:18PM -1000, Zachary Amsden wrote: > Attempt to synchronize TSCs which are reset to the same value. In the > case of a reliable hardware TSC, we can just re-use the same offset, but > on non-reliable hardware, we can get closer by adjusting the offset to > match the elapsed time. > > Signed-off-by: Zachary Amsden > --- > arch/x86/kvm/x86.c | 34 ++++++++++++++++++++++++++++++++-- > 1 files changed, 32 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 8e836e9..cedb71f 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -937,14 +937,44 @@ static inline void kvm_request_guest_time_update(struct kvm_vcpu *v) > set_bit(KVM_REQ_CLOCK_SYNC, &v->requests); > } > > +static inline int kvm_tsc_reliable(void) > +{ > + return (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && > + boot_cpu_has(X86_FEATURE_NONSTOP_TSC) && > + !check_tsc_unstable()); > +} > + why can't we re-use vmware TSC_RELIABLE flag?