[kudu-CR] system ntp: wait for sync via kernel

["Adar Dembo (Code Review)" <ge...@cloudera.org>]

Hello Will Berkeley, Kudu Jenkins, Todd Lipcon, 

I'd like you to reexamine a change. Please visit

    http://gerrit.cloudera.org:8080/13323

to look at the new patch set (#2).

Change subject: system_ntp: wait for sync via kernel
......................................................................

system_ntp: wait for sync via kernel

We've been having more and more trouble with dist-test slave clocks becoming
desynchronized. Because slaves run inside docker containers, we can't use
ntpd/chrony-based tools such as ntp-wait to wait for synchronization.
Moreover, this highlights a general issue with the existing wait-for-sync
approach: we can't differentiate between environments where ntpd isn't
running but should be, and environments where it's not but synchronization
is still expected.

This patch switches from ntp-wait and friends to ntp_adjtime-based waiting.
Originally it also cut the wait time from 60s to 30s (as an overture for
users running in the first environment who would prefer not to wait a full
minute to know that their ntpd isn't running), but this proved to be
insufficient to ride out dist-test clock desynchronization.

I also looked at the source code for ntp-wait and chronyc, but didn't see
them doing anything fundamentally more interesting than what we're now
doing with ntp_adjtime.

Change-Id: Ic133c4f9b5fd933216fb27f9f01396a5fee8276b
---
M src/kudu/clock/system_ntp.cc
1 file changed, 18 insertions(+), 27 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/23/13323/2
-- 
To view, visit http://gerrit.cloudera.org:8080/13323
To unsubscribe, visit http://gerrit.cloudera.org:8080/settings

Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Ic133c4f9b5fd933216fb27f9f01396a5fee8276b
Gerrit-Change-Number: 13323
Gerrit-PatchSet: 2
Gerrit-Owner: Adar Dembo <ad...@cloudera.com>
Gerrit-Reviewer: Adar Dembo <ad...@cloudera.com>
Gerrit-Reviewer: Kudu Jenkins (120)
Gerrit-Reviewer: Todd Lipcon <to...@apache.org>
Gerrit-Reviewer: Will Berkeley <wd...@gmail.com>