From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58516) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WrmfL-0007wQ-M2 for qemu-devel@nongnu.org; Tue, 03 Jun 2014 07:14:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WrmfE-0006IU-2A for qemu-devel@nongnu.org; Tue, 03 Jun 2014 07:14:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11535) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WrmfD-0006Hk-JW for qemu-devel@nongnu.org; Tue, 03 Jun 2014 07:13:55 -0400 Message-ID: <538DADED.4040609@redhat.com> Date: Tue, 03 Jun 2014 13:13:49 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1400253321-9239-1-git-send-email-agraf@suse.de> <538CDF30.9050902@beyond.pl> <20140603051630.GA2289@amt.cnet> In-Reply-To: <20140603051630.GA2289@amt.cnet> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v2] kvmclock: Ensure time in migration never goes backward List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marcelo Tosatti , =?UTF-8?B?TWFyY2luIEdpYnXFgmE=?= Cc: Alexander Graf , qemu-devel@nongnu.org Il 03/06/2014 07:16, Marcelo Tosatti ha scritto: > On Mon, Jun 02, 2014 at 10:31:44PM +0200, Marcin Gibu=C5=82a wrote: >>> + cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time)= ); >>> + >>> + delta =3D migration_tsc - time.tsc_timestamp; >> >> Hi, >> >> when I was testing live storage migration with libvirt I found out >> that this patch can cause virtual machine to hang when completing >> mirror job. >> >> This is (probably) because kvmclock_current_nsec() is called twice >> in a row and on second call time.tsc_timestamp is larger than >> migration_tsc. This causes delta to be huge and sets timer to >> invalid value. >> >> The double call happens when switching from old to new disk >> (pivoting in libvirt's nomenclature). >> >> Example values: >> >> First call: migration_tsc: 12052203518652476, time_tsc: >> 12052203301565676, delta 108543400 >> >> Second call: migration_tsc: 12052203518652476, time_tsc: >> 12052204478600322, delta 9223372036374801885 >> >> Perhaps it is worth adding: >> >> if (time.tsc_timestamp > migration_tsc) { >> return 0; >> } >> >> there? Untested though... > > Hi Marcin, > > Can you give this patch a try? Should read the guest TSC values after > stopping the VM. > > > diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c > index 6f4ed28a..bef2504 100644 > --- a/hw/i386/kvm/clock.c > +++ b/hw/i386/kvm/clock.c > @@ -17,6 +17,7 @@ > #include "qemu/host-utils.h" > #include "sysemu/sysemu.h" > #include "sysemu/kvm.h" > +#include "sysemu/cpus.h" > #include "hw/sysbus.h" > #include "hw/kvm/clock.h" > > @@ -65,6 +66,7 @@ static uint64_t kvmclock_current_nsec(KVMClockState *= s) > > cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time)); > > + assert(time.tsc_timestamp <=3D migration_tsc); > delta =3D migration_tsc - time.tsc_timestamp; > if (time.tsc_shift < 0) { > delta >>=3D -time.tsc_shift; > @@ -123,6 +125,8 @@ static void kvmclock_vm_state_change(void *opaque, = int running, > if (s->clock_valid) { > return; > } > + > + cpu_synchronize_all_states(); > ret =3D kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data); > if (ret < 0) { > fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret= )); > Can you send it with a real commit message? Paolo