Re： RE: Re： Re: [Xen-devel] when timer go back in dom0 save and

F.Y.I

>>> "Tian, Kevin" 08.11.27. 11:50 >>>

Sorry for a typo. I did mean domU instead of dom0. :-) The point here is that time_resume will sync to new system time and wall clock at restore, and thus pv guest should be able to continue... Xen system time is not wallclock time which just counts up from power up. As Keir points out, only its progress is used to drive internal jiffies.

--- Actually, save/restore or migrate will not call time_resume, this function mybe only be called in power saving.

Then what do you mean for "system time stop" here? TOD at user level, or within kernel you observe xen system time never changing?

--- If you run command "date" in user mode, you will find the date of output never change until a time interval equal to the value of time delay. And also, you can run some applicatin without many relation with time. such as vi,cd...etc, but if you run ping x.x.x.x you will find only one line's respose and never go on.

Thanks
--James

From: James Song [mailto:jsong@xxxxxxxxxx]
Sent: Thursday, November 27, 2008 11:20 AM
To: keir.fraser@xxxxxxxxxxxxx; Tian, Kevin; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: 答复： Re: [Xen-devel] when timer go back in dom0 save and restore ormigrate, PV domain hung

Hi,
    yes, there is a patch before to fix problem wc_sec/wc_nsec in xc_domain_restore.c, but it still missed something.
If constucting dom0 or restoring of a PV dom. Guest os will read the local wc_sec from xen as it base time.wc_sec is initialized with CMOS data. There were some case which wc_sec will be changed. One is that go back dom0's system-time will change dom0's time and wc_sec smaller which is both Guest os and Xen. Actually, we can do a simple test, starting a pv domain, then change dom0's time, and you will find the system time of guest os stopped. That because you change wc_sec of both xen and guest os.
    This patch only consider the case of save/restore. I still not sure the policy of this case that is when dom0's system-time go back. what VMs should do? So, I have add this case to this patch
   By the way, Kevin, Guest OS will hang not dom0 ;-) and also the time of hang just is equivlant to the time interval you go back in dom0 or new machine you migrate.
Thanks
-- James

>>> Keir Fraser 08?11?26? ?? 22:58 >>> So what happens if someone changes wallclock using 'date'? That's basically kind of what will appear to happen when s/r occurs.

-- Keir

On 26/11/08 14:32, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

hrtimer supports two timer bases: CLOCK_MONOTONIC and CLOCK_REALTIME. wall_to_monotonic is only added in former case, and for latter instead TOD is used directly per my reading. I did a quick search, and it looks that futex and ntp are using CLOCK_REALTIME. Also there's one vsyscall gate which can pass CLOCK_REALTIME from caller too.

Thanks,
Kevin

From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
Sent: Wednesday, November 26, 2008 10:26 PM
To: Tian, Kevin; 'James Song'; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] when timer go back in dom0 save and restore or migrate, PV domain hung

hrtimers add wall_to_monotonic to xtime to get a timesource that doesn't (or shouldn't!) warp.

-- Keir

On 26/11/08 14:20, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

how about hrtimers? one mode is CLOCK_REALTIME, which uses getnstimeofday as expiration. Once system time is changed either in local or new machine, that expiration can't be adjusted. but i'm not sure whether it still makes sense to try hrtimers in a guest.

Thanks
Kevin

From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
Sent: Wednesday, November 26, 2008 10:11 PM
To: Tian, Kevin; 'James Song';   xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] when timer go back in dom0 save and restore or migrate, PV domain hung

The problem hasn't been fully explained, but I can say that PV guests expect system time to jump across s/r and deal with that. For   example, Linux doesn't use Xen system time internally, but uses its progress to periodically update jiffies, which does not warp across s/r.

We have had problems corrupting wc_sec/wc_nsec in xc_domain_restore.c, but that was fixed some time ago.

-- Keir

On 26/11/08 14:00, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

This is not a s/r or lm specific issue. For example, system time can be changed even when pv guest is running. Your patch only hacks restore point once, and wc_sec can still be changed later when system time is changed on-the-fly again.

IIRC, pv guest can catch up wall clock change in timer interrupt, and time_resume will sync internal processed system time with new system time after restored. But I'm not sure whether it's enough. Actually the more interesting is the uptime difference. For example, timer with expiration calculated on previous system time may wait nearly infinite if uptime among two boxes vary a lot. But I think such issue should have been considered   already, e.g. some user tool assistance. I think Keir can comment better here.

BTW, do you happen to know what exactly dom0 hangs on? In some busy loop to catch up time, or long delay to some critical timer expiration?

Thanks,
Kevin

From:   xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx]   On Behalf Of James Song
Sent: Tuesday, November 25, 2008 4:02 PM
To:    xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] when timer go back in dom0 save and restore or migrate, PV domain hung

Hi,
   I   find PV domin hung, When we take those steps
         1, save PV domain
         2,   change system time of PV domain back
         3, restore   a PV domain
        or
         1, migrate a PV domain from Machine A to Machine   B
         2, the system   time of Machine B is slower than Machine A.
   the problem is wc_sec will be change when system-time chanaged in dom0 or restore in a   slower-system-time machine, but when restoring, xen don't restore the wc_sec of share_info from xenstore and use native   one. So guest os will hang.
this patch will work for this issue.

Thanks
-- Song   Wei

diff -r a5ed0dbc829f tools/libxc/xc_domain_restore.c
---    a/tools/libxc/xc_domain_restore.c    Tue Nov 18 14:34:14 2008 +0800
+++ b/tools/libxc/xc_domain_restore.c     Fri Nov 21   17:34:15 2008 +0800
@@ -328,6 +328,16   @@

     /* For info   only */
     nr_pfns = 0;
+       //jsong@xxxxxxxxxx, james song
+      memset(&domctl, 0,   sizeof(domctl));
+     domctl.domain =   dom;
+     domctl.cmd    =    XEN_DOMCTL_restoredomain;
+    frc =   do_domctl(xc_handle, &domctl);
+     if ( frc != 0 )
+      {
+               ERROR("Unable   to set flag of restore.");
+               goto   out;
+      }

     if (   read_exact(io_fd, &p2m_size, sizeof(unsigned long))    )
     {
@@ -1120,6 +1130,8    @@

     /* restore saved vcpu_info and arch specific info   */
     MEMCPY_FIELD(new_shared_info,    old_shared_info, vcpu_info);
+       MEMCPY_FIELD(new_shared_info, old_shared_info,   wc_nsec);
+     MEMCPY_FIELD(new_shared_info,    old_shared_info,   wc_sec);
      MEMCPY_FIELD(new_shared_info,   old_shared_info,    arch);

     /* clear any pending events and the selector */
diff -r a5ed0dbc829f xen/arch/x86/time.c
---   a/xen/arch/x86/time.c     Tue Nov 18 14:34:14 2008 +0800
+++   b/xen/arch/x86/time.c     Fri Nov 21 17:34:15 2008 +0800
@@   -689,7 +689,6   @@
      wmb();
     (*version)++;
}
-
void    update_vcpu_system_time(struct vcpu   *v)
{
      struct cpu_time        *t;
@@ -703,7 +702,6   @@

     if (   u->tsc_timestamp == t->local_tsc_stamp   )
          return;
-
      version_update_begin(&u->version);

      u->tsc_timestamp       = t->local_tsc_stamp;
@@   -713,14 +711,19   @@

      version_update_end(&u->version);
}
-
void    update_domain_wallclock_time(struct domain    *d)
{
      spin_lock(&wc_lock);
+      if(d->after_restore )
+      {
+           d->after_restore = 0;
+        goto   out; //jsong@xxxxxxxxxx
+      }
      version_update_begin(&shared_info(d,    wc_version));
     shared_info(d,   wc_sec) = wc_sec +   d->time_offset_seconds;
     shared_info(d,    wc_nsec) =   wc_nsec;
      version_update_end(&shared_info(d,    wc_version));
+out:
      spin_unlock(&wc_lock);
}

@@   -751,7 +754,6 @@
     u64   x;
     u32 y, _wc_sec,   _wc_nsec;
     struct domain    *d;
-
     x = (secs * 1000000000ULL) + (u64)nsecs -   system_time_base;
     y = do_div(x, 1000000000);

@@ -1050,7 +1052,6   @@
struct tm    wallclock_time(void)
{
     uint64_t    seconds;
-
     if ( !wc_sec    )
         return   (struct tm) { 0 };

diff -r a5ed0dbc829f   xen/common/domctl.c
--- a/xen/common/domctl.c      Tue Nov 18 14:34:14 2008 +0800
+++    b/xen/common/domctl.c    Fri Nov 21 17:34:15 2008 +0800
@@ -24,7 +24,6 @@
#include   <asm/current.h>
#include    <public/domctl.h>
#include    <xsm/xsm.h>
-
extern long    arch_do_domctl(
     struct xen_domctl *op, XEN_GUEST_HANDLE(xen_domctl_t) u_domctl);

@@ -315,6 +314,16    @@
         ret =    0;
     }
      break;
+     case XEN_DOMCTL_restoredomain:
+     {
+          struct domain   *d;
+         if ( (d =   rcu_lock_domain_by_id(op->domain)) == NULL   )
+               break;
+
+          d->after_restore =    1;
+           rcu_unlock_domain(d);
+           break;
+     }

     case    XEN_DOMCTL_createdomain:
     {
diff   -r a5ed0dbc829f xen/include/public/domctl.h
---    a/xen/include/public/domctl.h    Tue Nov 18 14:34:14 2008 +0800
+++ b/xen/include/public/domctl.h      Fri Nov 21 17:34:15 2008 +0800
@@ -61,6 +61,7 @@
#define XEN_DOMCTL_destroydomain        2
#define    XEN_DOMCTL_pausedomain           3
#define   XEN_DOMCTL_unpausedomain        4
+#define   XEN_DOMCTL_restoredomain         51
#define   XEN_DOMCTL_resumedomain         27

#define    XEN_DOMCTL_getdomaininfo       5
diff -r   a5ed0dbc829f xen/include/xen/sched.h
---   a/xen/include/xen/sched.h     Tue Nov 18 14:34:14 2008   +0800
+++ b/xen/include/xen/sched.h    Fri Nov 21 17:34:15   2008 +0800
@@ -231,6 +231,7   @@
      * cause a   deadlock. Acquirers don't spin waiting; they    preempt.
      */
      spinlock_t   hypercall_deadlock_mutex;
+    int after_restore;    //jsong@xxxxxxxxxx
};

struct    domain_setup_info
---------------------------------------------------------------------------------------------
Thanks
--Song    wei

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Re： RE: Re： Re: [Xen-devel] when timer go back in dom0 save and restore