From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: kvmclock doesn't work, help? Date: Wed, 9 Dec 2015 13:10:59 -0800 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 To: kvm list , Marcelo Tosatti , Radim Krcmar , Paolo Bonzini , X86 ML Return-path: Received: from mail-oi0-f45.google.com ([209.85.218.45]:36729 "EHLO mail-oi0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751321AbbLIVLU (ORCPT ); Wed, 9 Dec 2015 16:11:20 -0500 Received: by oiww189 with SMTP id w189so33899988oiw.3 for ; Wed, 09 Dec 2015 13:11:19 -0800 (PST) Sender: kvm-owner@vger.kernel.org List-ID: I'm trying to clean up kvmclock and I can't get it to work at all. My host is 4.4.0-rc3-ish on a Skylake laptop that has a working TSC. If I boot an SMP (2 vcpus) guest, tracing says: qemu-system-x86-2517 [001] 102242.610654: kvm_update_master_clock: masterclock 0 hostclock tsc offsetmatched 0 qemu-system-x86-2521 [000] 102242.613742: kvm_track_tsc: vcpu_id 0 masterclock 0 offsetmatched 0 nr_online 1 hostclock tsc qemu-system-x86-2522 [000] 102242.622959: kvm_track_tsc: vcpu_id 1 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc qemu-system-x86-2521 [000] 102242.645123: kvm_track_tsc: vcpu_id 0 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc qemu-system-x86-2522 [000] 102242.647291: kvm_track_tsc: vcpu_id 1 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc qemu-system-x86-2521 [000] 102242.653369: kvm_track_tsc: vcpu_id 0 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc qemu-system-x86-2522 [000] 102242.653429: kvm_track_tsc: vcpu_id 1 masterclock 0 offsetmatched 1 nr_online 2 hostclock tsc qemu-system-x86-2517 [001] 102242.653447: kvm_update_master_clock: masterclock 0 hostclock tsc offsetmatched 1 qemu-system-x86-2521 [000] 102242.653657: kvm_update_master_clock: masterclock 0 hostclock tsc offsetmatched 1 qemu-system-x86-2522 [002] 102242.664448: kvm_update_master_clock: masterclock 0 hostclock tsc offsetmatched 1 If I boot a UP guest, tracing says: qemu-system-x86-2567 [001] 102370.447484: kvm_update_master_clock: masterclock 0 hostclock tsc offsetmatched 1 qemu-system-x86-2571 [002] 102370.447688: kvm_update_master_clock: masterclock 0 hostclock tsc offsetmatched 1 I suspect, but I haven't verified, that this is fallout from: commit 16a9602158861687c78b6de6dc6a79e6e8a9136f Author: Marcelo Tosatti Date: Wed May 14 12:43:24 2014 -0300 KVM: x86: disable master clock if TSC is reset during suspend Updating system_time from the kernel clock once master clock has been enabled can result in time backwards event, in case kernel clock frequency is lower than TSC frequency. Disable master clock in case it is necessary to update it from the resume path. Signed-off-by: Marcelo Tosatti Signed-off-by: Paolo Bonzini Can we please stop making kvmclock more complex? It's a beast right now, and not in a good way. It's far too tangled with the vclock machinery on both the host and guest sides, the pvclock stuff is not well thought out (even in principle in an ABI sense), and it's never been clear to my what problem exactly the kvmclock stuff is supposed to solve. I'm somewhat tempted to suggest that we delete kvmclock entirely and start over. A correctly functioning KVM guest using TSC (i.e. ignoring kvmclock entirely) seems to work rather more reliably and considerably faster than a kvmclock guest. --Andy -- Andy Lutomirski AMA Capital Management, LLC