From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock Date: Mon, 19 Apr 2010 14:35:34 +0300 Message-ID: <4BCC4006.8000501@redhat.com> References: <1271356648-5108-1-git-send-email-glommer@redhat.com> <1271356648-5108-2-git-send-email-glommer@redhat.com> <4BCA026D.3070309@redhat.com> <1271673975.1674.763.camel@laptop> <1271674154.1674.771.camel@laptop> <4BCC3617.6050106@redhat.com> <1271674745.1674.802.camel@laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Glauber Costa , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Marcelo Tosatti , Zachary Amsden To: Peter Zijlstra Return-path: In-Reply-To: <1271674745.1674.802.camel@laptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 04/19/2010 01:59 PM, Peter Zijlstra wrote: > >> So what do we need? test for both TSC_RELIABLE and NONSTOP_TSC? IM= O >> TSC_RELIABLE should imply NONSTOP_TSC. >> =20 > Yeah, I think RELIABLE does imply NONSTOP and CONSTANT, but NONSTOP&& > CONSTANT does not make RELIABLE. > =20 The manual says: > 16.11.1 Invariant TSC > > The time stamp counter in newer processors may support an enhancement= ,=20 > referred > to as invariant TSC. Processor=E2=80=99s support for invariant TSC is= indicated by > CPUID.80000007H:EDX[8]. > The invariant TSC will run at a constant rate in all ACPI P-, C-. and= =20 > T-states. This is > the architectural behavior moving forward. On processors with=20 > invariant TSC > support, the OS may use the TSC for wall clock timer services (instea= d=20 > of ACPI or > HPET timers). TSC reads are much more efficient and do not incur the=20 > overhead > associated with a ring transition or access to a platform resource. and this maps to NONSTOP, so I think we're fine. --=20 error compiling committee.c: too many arguments to function