And I almost forgot, since you have NTP running on both, you could even setup one of them as NTP server for the other. Which will give you a good way to get the offset between them using the same way as described above.
Christian Ehrhardt Software Engineer, Ubuntu Server Canonical Ltd On Thu, Jul 21, 2016 at 10:14 AM, Christian Ehrhardt < [email protected]> wrote: > Hi, > as Michael already mentioned the guests only have a offset they can store > in the SIEBK. > The clock of all your guests are ticking at the same pace, so you have no > traditional different drifting due to different clocks on one system z box. > If you have a difference between your Linux Guests that should be from > your Linux actually setting time (and by that actually their offset). > Given the permissions and access one could surely check the offsets of > both guests, but that can be quite hard :-) > > For all other checks the issue will almost always be, that you would have > to send a command to both at the same time which is impossible - so you can > never compare most of the output if they just report "date" or such. > But NTP which you already have running can help you to find if those two > systems are apart. > > If you run "ntpq -pn" you get a list of servers as configured and an > offset of your system too them. > Now since your Linux guests are ticking at the same rate by the HW design, > the offset to the same NTP peers should stay the same. > > If these offsets differ on your systems, something on that system has set > time to be that offset. > > Also, if you continue debugging this I'd recommend trying to stay away > from high level things like "date" as there are so many levels in between > which could skew things. > Write a minimal program calling STCKE should be way more reliable. > And if you find the difference is always zero on STCKE level, but once you > move to more abstracted functions like clock_gettimeofday / gettimeofday > you can start debugging down that route. > > Kind Regards, > Christian > > Christian Ehrhardt > Software Engineer, Ubuntu Server > Canonical Ltd > > On Thu, Jul 21, 2016 at 1:18 AM, Marcy Cortes < > [email protected]> wrote: > >> I used a rexx exec to send commands to the console (secuser) that looked >> like this: >> >> /**/ >> address command "CP SEND ZLA226 date +'%d/%m/%Y %H:%M:%S:%6N'" >> address command "CP SEND ZLA247 date +'%d/%m/%Y %H:%M:%S:%6N'" >> >> I would expect ZLA247's to be a bit later, but sometimes it shows earlier. >> >> 18:04:34 20/07/2016 18:04:34:735597 >> 18:04:34 20/07/2016 18:04:34:737365 >> >> 18:06:42 20/07/2016 18:06:42:317457 >> 18:06:42 20/07/2016 18:06:42:325410 >> >> 18:08:50 20/07/2016 18:08:50:473232 >> 18:08:50 20/07/2016 18:08:50:467567 >> >> 18:13:51 20/07/2016 18:13:51:055624 >> 18:13:51 20/07/2016 18:13:51:037563 >> >> Hmm. >> >> -----Original Message----- >> From: Linux on 390 Port [mailto:[email protected]] On Behalf Of >> Michael Harding >> Sent: Wednesday, July 20, 2016 2:47 PM >> To: [email protected] >> Subject: Re: [LINUX-390] Back to the future? >> >> In the guests' VMDBKs, in the SIEBK is stored the offset from the >> hardware clock that gets loaded when the guest is run. I don't recall the >> offset in the block. Unless that's different they should both be seeing >> the same CPU clock. >> >> -- >> Mike Harding >> z/VM System Support >> /sp >> >> >> Linux on 390 Port <[email protected]> wrote on 07/20/2016 01:42:05 >> PM: >> >> > From: Marcy Cortes <[email protected]> >> > To: [email protected] >> > Date: 07/20/2016 01:42 PM >> > Subject: Back to the future? >> > Sent by: Linux on 390 Port <[email protected]> >> > >> > So we have some servers that pass timestamps around to see how long >> > they have to do something before throwing in the towel. >> > >> > They've recently put in some logging to debug some errors and have >> > found some cases of going back in time. >> > >> > TmsSent 2016-07-20 07:40:07.000034 | TrapRx 2016-07-20 07:40:06.000944 >> > >> > So back in time by nearly a second (.99909). >> > >> > These 2 servers are on the same VM system. Both run NTP. >> > We know things get really out of whack without NTP. We had a bug >> > where it didn't start and things got really confused. >> > >> > Could NTP be misbehaving? It was just patched. How can I prove >> > that the clocks on the 2 servers have a different time so that I can >> > ascertain if it is NTP or something else. >> > >> > >> > >> > Marcy >> > >> > >> > >> > ---------------------------------------------------------------------- >> > For LINUX-390 subscribe / signoff / archive access instructions, send >> > email to [email protected] with the message: INFO LINUX-390 or >> visit >> > http://www.marist.edu/htbin/wlvindex?LINUX-390 >> > ---------------------------------------------------------------------- >> > For more information on Linux on System z, visit >> > http://wiki.linuxvm.org/ >> > >> >> ---------------------------------------------------------------------- >> For LINUX-390 subscribe / signoff / archive access instructions, send >> email to [email protected] with the message: INFO LINUX-390 or visit >> http://www.marist.edu/htbin/wlvindex?LINUX-390 >> ---------------------------------------------------------------------- >> For more information on Linux on System z, visit http://wiki.linuxvm.org/ >> >> ---------------------------------------------------------------------- >> For LINUX-390 subscribe / signoff / archive access instructions, >> send email to [email protected] with the message: INFO LINUX-390 or >> visit >> http://www.marist.edu/htbin/wlvindex?LINUX-390 >> ---------------------------------------------------------------------- >> For more information on Linux on System z, visit >> http://wiki.linuxvm.org/ >> > > ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
