From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [RFC PATCH v2 1/2] add support for Hyper-V reference time counter Date: Thu, 23 May 2013 15:40:23 +0200 Message-ID: <519E1C47.3070700@redhat.com> References: <1368947197-9033-1-git-send-email-vrozenfe@redhat.com> <1368947197-9033-2-git-send-email-vrozenfe@redhat.com> <20130522004614.GA7322@amt.cnet> <745195650.5763962.1369207977883.JavaMail.root@redhat.com> <519D3ED6.8010804@redhat.com> <519DB495.8040708@dlhnet.de> <1203166753.6432195.1369311921642.JavaMail.root@redhat.com> <519E172A.9040706@redhat.com> <519E179F.6000307@dlhnet.de> <519E1848.9010200@redhat.com> <519E1A09.5080601@dlhnet.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Vadim Rozenfeld , Marcelo Tosatti , kvm@vger.kernel.org, gleb@redhat.com, pl@dlh.net To: Peter Lieven Return-path: Received: from mx1.redhat.com ([209.132.183.28]:53070 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758671Ab3EWNke (ORCPT ); Thu, 23 May 2013 09:40:34 -0400 In-Reply-To: <519E1A09.5080601@dlhnet.de> Sender: kvm-owner@vger.kernel.org List-ID: Il 23/05/2013 15:30, Peter Lieven ha scritto: >>>> So I would prefer to remove kvm->arch.hv_ref_count altogether. >>> >>> But only if the migration support is guaranteed. >> >> Migration support wouldn't work yet anyway, you need to recompute the >> scale and sequence. But that could be done by KVM_SET_CLOCK. > > hv_ref_counter does work out of the box. what I was trying to say is > even it is slower than iTSC, it is significantly faster than hpet > or pmtimer and I can confirm it works flawlessly with migration. I can't see how without a userspace patch to migrate hv_ref_count. >>> And what if we have a host which lacks invariant TSC support? >> >> Then the sequence must be set to 0 or 0xFFFFFFFF, I still haven't >> understood. :) > > yes, but windows does then fall back to pmtimer or hpet which is much > slower then reference counter. IIUC, with 0 it doesn't. Paolo