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[Bug 545191] ntpd sync fails/noisy with kernel-xen (clocksource = jiffies); works as expected with kernel-default (clocksource = hpet)
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Thu, 15 Oct 2009 10:27:16 -0600
  • Message-id: <20091015162716.DD4A7245517@xxxxxxxxxxxxxxxxxxxxxx>

User added comment

--- Comment #6 from account disabled <> 2009-10-15 10:27:11
MDT ---
(In reply to comment #5)
With "others" I don't mean people using other distros - SLE11 is working fine
for them, and as long as you use an up-to-date kernel, that's gonna be the
as SLE11's.

then more confusion ... something in my env is consistently problematic. i've
now chatted with enough people across multiple distros, hardware, configs, etc
to know that problems with timekeeping in xen are not uncommon. the whole
business seems a bit of a mess, atm ...

in the Dom0 case, i suspect? captured via serial port? or are dmesg & xm
output sufficient?

xm dmesg output will be sufficient if you make sure the log level is high
enough, and no messages are discarded.

dmesg won't be enough - it's mainly the boot messages I'm after (i.e.

i'll put that together in a minute, and post ...

But you asking this question makes me ask another one: Are you seeing this
issue in Dom0, DomU, or both?


the problem i've reported above/here is 'just' Dom0. in DomU, if:

/proc/sys/xen/independent_wallclock --> 0
/sys/devices/system/clocksource/clocksource0/current_clocksource --> xen

then, of course, DomU simply tracks Dom0. checking sync between the two, DomU
tracks Dom0 faithfully, without problem, in this case.

in the DomU (paravirt) case where i've independent, ntp-driven clock, with,

/proc/sys/xen/independent_wallclock --> 1
/sys/devices/system/clocksource/clocksource0/current_clocksource --> jiffies

the DomU jitter is somewhat worse than the Dom0 jitter. and, as one might
expect, sync is just as elusive.

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