From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim Krcmar Subject: Re: What's kvmclock's custom sched_clock for? Date: Thu, 7 Jan 2016 18:48:01 +0100 Message-ID: <20160107174800.GB12375@potion.brq.redhat.com> References: <20160107151810.GA12375@potion.brq.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Marcelo Tosatti , kvm list To: Andy Lutomirski Return-path: Received: from mx1.redhat.com ([209.132.183.28]:49322 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751220AbcAGRsE (ORCPT ); Thu, 7 Jan 2016 12:48:04 -0500 Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: 2016-01-07 09:27-0800, Andy Lutomirski: > On Thu, Jan 7, 2016 at 7:18 AM, Radim Krcmar wrote: > > 2016-01-07 00:41-0800, Andy Lutomirski: >>> This still doesn't explain why even explicitly trying to set invtsc >>> doesn't seem to work. >> >> Seems like a bug. Mine cpuid is >> 0x80000007 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 edx=0x00000100 >> and QEMU says >> warning: host doesn't support requested feature: CPUID.80000007H:EDX.invtsc [bit 8] >> >> I'll see if it's in KVM or QEMU. (We should only forbid migrations to >> hosts with different frequency and without guest TSC scaling.) > > If I do -cpu host,migratable=off,+invtsc, then it works. Maybe QEMU > is just being too strict. This is Skylake. It does, thanks. It's mainly a misleading warning then; stripping flags at the beginning instead of denying migration later on makes some sense.