From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH v2 0/3] x86/vdso: Add Hyper-V TSC page clocksource support Date: Tue, 14 Feb 2017 15:56:08 +0100 (CET) Message-ID: References: <20170214124408.25931-1-vkuznets@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170214124408.25931-1-vkuznets@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Vitaly Kuznetsov Cc: Stephen Hemminger , Haiyang Zhang , x86@kernel.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Ingo Molnar , "H. Peter Anvin" , devel@linuxdriverproject.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Tue, 14 Feb 2017, Vitaly Kuznetsov wrote: > Hi, > > while we're still waiting for a definitive ACK from Microsoft that the > algorithm is good for SMP case (as we can't prevent the code in vdso from > migrating between CPUs) I'd like to send v2 with some modifications to keep > the discussion going. Migration is irrelevant. The TSC page is guest global so updates will happen on some (random) host CPU and therefor you need the usual barriers like we have them in our seqcounts unless an access to the sequence will trap into the host, which would defeat the whole purpose of the TSC page. Thanks, tglx