Change in vdsm[master]: virt: vm: Replace update time migration TODO

mzamazal at redhat.com mzamazal at redhat.com
Tue Dec 15 09:56:39 UTC 2015


Milan Zamazal has uploaded a new change for review.

Change subject: virt: vm: Replace update time migration TODO
......................................................................

virt: vm: Replace update time migration TODO

As discussed in https://gerrit.ovirt.org/49212, we are not going to
update time on the guest after live migration.  So we replace the
corresponding TODO with an explanation comment.

Change-Id: Ic2f6419825973680b2188ffa34e80994a1fbdb18
Signed-off-by: Milan Zamazal <mzamazal at redhat.com>
---
M vdsm/virt/vm.py
1 file changed, 11 insertions(+), 5 deletions(-)


  git pull ssh://gerrit.ovirt.org:29418/vdsm refs/changes/99/50499/1

diff --git a/vdsm/virt/vm.py b/vdsm/virt/vm.py
index b375cd0..28c0019 100644
--- a/vdsm/virt/vm.py
+++ b/vdsm/virt/vm.py
@@ -2831,11 +2831,17 @@
                 hooks.after_device_migrate_destination(
                     dev._deviceXML, self.conf, dev.custom)
 
-            # TODO: _syncGuestTime() should be called here as it is in
-            # restore_state path.  But there may be some issues with the call
-            # such as blocking for some time when qemu-guest-agent is not
-            # running in the guest.  We'd like to discuss them more before
-            # touching migration.
+            # We refrain from syncing time in this path.  There are two basic
+            # reasons:
+            # 1. The jump change in the time (as performed by QEMU) may cause
+            #    undesired effects like unnecessary timeouts, false alerts
+            #    (think about logging excessive SQL command execution times),
+            #    etc.  This is not what users expect when performing live
+            #    migrations.
+            # 2. The user can simply run NTP on the VM to keep the time right
+            #    and smooth after migrations.  On the contrary to suspensions,
+            #    there is no danger of excessive delays preventing NTP from
+            #    operation.
 
         if 'guestIPs' in self.conf:
             del self.conf['guestIPs']


-- 
To view, visit https://gerrit.ovirt.org/50499
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Gerrit-MessageType: newchange
Gerrit-Change-Id: Ic2f6419825973680b2188ffa34e80994a1fbdb18
Gerrit-PatchSet: 1
Gerrit-Project: vdsm
Gerrit-Branch: master
Gerrit-Owner: Milan Zamazal <mzamazal at redhat.com>


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