James Song
2008-Nov-27 03:19 UTC
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 <keir.fraser@eu.citrix.com> 08年11月26日 下午 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@intel.com> 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
mailto:keir.fraser@eu.citrix.com]
Sent: Wednesday, November 26, 2008 10:26 PM
To: Tian, Kevin; ''James Song''; xen-devel@lists.xensource.com
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@intel.com> 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
mailto:keir.fraser@eu.citrix.com]
Sent: Wednesday, November 26, 2008 10:11 PM
To: Tian, Kevin; ''James Song'';
xen-devel@lists.xensource.com
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@intel.com> 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?
Sent: Tuesday, November 25, 2008 4:02 PM
To: xen-devel@lists.xensource.com
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@novell.com, 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@novell.com
+ }
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)) == N+
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@novell.com
};
struct domain_setup_info
---------------------------------------------------------------------------------------------
Thanks
--Song wei
</keir.fraser@eu.citrix.com>
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel
Tian, Kevin
2008-Nov-27 03:50 UTC
RE: 答复： Re: [Xen-devel] when timer go back in dom0 save and restore ormigrate, PV domain hung
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.
Then what do you mean for "system time stop" here? TOD at user level,
or within kernel you observe xen system time never changing?
Thanks,
Kevin
________________________________
From: James Song [mailto:jsong@novell.com]
Sent: Thursday, November 27, 2008 11:20 AM
To: keir.fraser@eu.citrix.com; Tian, Kevin; xen-devel@lists.xensource.com
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@intel.com> 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@eu.citrix.com]<mailto:keir.fraser@eu.citrix.com%5D>
Sent: Wednesday, November 26, 2008 10:26 PM
To: Tian, Kevin; 'James Song'; xen-devel@lists.xensource.com
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@intel.com> 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@eu.citrix.com]<mailto:keir.fraser@eu.citrix.com%5D>
Sent: Wednesday, November 26, 2008 10:11 PM
To: Tian, Kevin; 'James Song'; xen-devel@lists.xensource.com
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@intel.com> 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@lists.xensource.com
[mailto:xen-devel-bounces@lists.xensource.com]<mailto:xen-devel-bounces@lists.xensource.com%5D>
On Behalf Of James Song
Sent: Tuesday, November 25, 2008 4:02 PM
To: xen-devel@lists.xensource.com
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@novell.com, 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@novell.com
+ }
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@novell.com
};
struct domain_setup_info
---------------------------------------------------------------------------------------------
Thanks
--Song wei
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Xen-devel@lists.xensource.com
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