I've performed this test on two VMs, which it's my understanding are
both PV, 32-bits and compiled from the 2.6.18. I am using Citrix's
XenEnterprise 4.1.0 software and you can see its VM's configuration
below, giving the version and the PV bootloader.
I applied your changes to the grub line but I don't believe it is
taking:
Prior to application:
p20deb:~# cat
/sys/devices/system/clocksource/clocksource0/current_clocksource
jiffies
after "clock=pit" added to my grub line
titleDebian GNU/Linux, kernel xenu-2.6.18.xs4.1.0.1168.6013
root(hd0,0)
kernel/boot/vmlinuz-xenu-2.6.18.xs4.1.0.1168.6013 root=/dev/xvda1 ro
time clock=pit
savedefault
p20deb:~# cat
/sys/devices/system/clocksource/clocksource0/current_clocksource
jiffies
I ran the test with clock=pit and it still drifted
[root@p20xen1 ~]# xe vm-list name-label=Debian\ Etch\ 4.0\ \(1\) params=
uuid ( RO) :
bc40e67c-2f85-5be1-66ef-31ae3b2ab8b3
name-label ( RW): Debian Etch 4.0 (1)
name-description ( RW):
user-version ( RW): 1
is-a-template ( RW): false
is-control-domain ( RO): false
power-state ( RO): halted
memory-dynamic-max ( RW): 268435456
memory-dynamic-min ( RW): 268435456
memory-static-max ( RW): 268435456
memory-static-min ( RW): 16777216
suspend-VDI-uuid ( RO): <not in database>
VCPUs-params (MRW):
VCPUs-max ( RW): 1
VCPUs-at-startup ( RW): 1
actions-after-shutdown ( RW): Destroy
actions-after-reboot ( RW): Restart
actions-after-crash ( RW): Restart
console-uuids (SRO):
ecf5b121-6a0b-9a6d-fb98-62c608afaa24
platform (MRW): nx: false; acpi: true; apic: true;
pae: true
allowed-operations (SRO): clone; start; start_on; export;
destroy; make_into_template
current-operations (SRO):
allowed-VBD-devices (SRO): <expensive field>
allowed-VIF-devices (SRO): <expensive field>
possible-hosts ( RO): <expensive field>
HVM-boot-policy ( RW):
HVM-boot-params (MRW):
HVM-shadow-multiplier ( RW): 1.000
PV-kernel ( RW):
PV-ramdisk ( RW):
PV-args ( RW):
PV-legacy-args ( RW):
PV-bootloader ( RW): pygrub
PV-bootloader-args ( RW):
last-boot-CPU-flags ( RO):
resident-on ( RO): <not in database>
affinity ( RW):
1c29b960-78b2-46cc-a808-8cb454a3cece
other-config (MRW): last_shutdown_time:
20080612T20:16:56Z; last_shutdown_action: Restart;
last_shutdown_initiator: internal; last_shutdown_reason: rebooted;
linux_template: true; mac_seed: e381c9e3-0346-09d6-d92e-815f5267bbf8
dom-id ( RO): -1
recommendations ( RO): <restrictions><restriction
field="memory-static-max" max="34359738368" /><restriction
field="vcpus-max" max="8" /><restriction property="number-of-vbds"
max="7" /><restriction property="number-of-vifs" max="7"
/></restrictions>
xenstore-data (MRW):
start-time ( RO): <unknown time>
install-time ( RO): <unknown time>
memory-actual ( RO): <not in database>
VCPUs-number ( RO): <not in database>
VCPUs-utilisation (MRO): <not in database>
vm-metrics-last-updated ( RO): <not in database>
os-version (MRO): name: Debian 4.0; uname:
2.6.18.xs4.1.0.1168.6013; distro: debian; major: 4; minor: 0
PV-drivers-version (MRO): major: 4; minor: 1; micro: 0
PV-drivers-up-to-date ( RO): true
memory (MRO):
disks (MRO):
networks (MRO):
other (MRO):
guest-metrics-last-updated ( RO): 19700101T00:00:00Z
-----Original Message-----
From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
Sent: Friday, June 13, 2008 4:06 PM
To: Roger Cruz; xen-devel
Subject: RE: [Xen-devel] Kernel printk timestamps and walltime drift
Hi Roger --
I'm assuming this is an hvm 32-bit 2.6.18 domain and you are
running on Xen 3.1.3 or newer?
If so, try setting clock=pit in your grub.conf file then
after boot test that it "took" with:
cat /sys/devices/system/clocksource/clocksource0/current_clocksource
If it is pit, try your test again.
Note that there's a lot of work going on trying to fix
hvm timer problems right now. There are many many different
cases because Linux has changed algorithms many times over
the history of 2.6.
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx]On Behalf Of Roger Cruz
> Sent: Friday, June 13, 2008 12:49 PM
> To: xen-devel
> Subject: [Xen-devel] Kernel printk timestamps and walltime drift
>
>
> <<Roger Cruz.vcf>> Hello fellow developers,
>
> I ran across a curious observation this week when trying to
> analyze the
> Debian 4.0 VM kernel's printk timestamps against walltime.
> It looks as
> if the kernel's timestamps are running slow.
>
> On a reference debian 4.0 VM (created from Citrix templates),
> I ran the
> following script after booting the OS with the "time" option
> in the grub
> boot line.
>
> You can see that the kernel time in the brackets (host up time in
> seconds) should have given us a difference of 3600 seconds
> when ran over
> an hr period. I, however, got 3592.770286, a slip of 7+
> seconds. I've
> ran a similar experiment and over the course of 12hrs, the kernel
> timestamps lose 97 seconds!
>
> So unless I'm misunderstanding the printk times, the problem is either
> with the way the Linux OS converts TSC cycles to seconds not
> being very
> accurate OR how the hypervisor feeds the VM-ified TSC counts to the
> guest VM.
>
> Note that I'm sure the walltime was correct as I could monitor the
> printed walltime against an atomic clock in another window
> and it always
> matched (within the precision of my eyes moving back and forth, of
> course).
>
> Have any of you seen something similar or have an explanation?
>
> grub line
> title Debian GNU/Linux, kernel xenu-2.6.18.xs4.1.0.1168.6013
> root (hd0,0)
> kernel /boot/vmlinuz-xenu-2.6.18.xs4.1.0.1168.6013 root=/dev/xvda1 ro
> time
> savedefault
>
> #/sbin/bash
> i="0"
> while [ $i -lt 10000 ]
> do
> date -u "+secs since 1970: %s, time:%c" > /dev/kmsg
> sleep 60
> i=$[$i + 1]
> done
>
> Reference Debian VM:
> end time 91158.761414 - start time 87565.991128 = 3592.770286. It
> should have been 3600 seconds
> Epoch time: 1213306731 - 1213303130 = 3601 close enough to 3600.
>
> p20deb:~# ./timetest
> [87565.991128] secs since 1970: 1213303130, time:Thu Jun 12 20:38:50
> 2008
> [87625.865258] secs since 1970: 1213303190, time:Thu Jun 12 20:39:50
> 2008
> [87685.745109] secs since 1970: 1213303250, time:Thu Jun 12 20:40:50
> 2008
> [87745.624397] secs since 1970: 1213303310, time:Thu Jun 12 20:41:50
> 2008
> [87805.504331] secs since 1970: 1213303370, time:Thu Jun 12 20:42:50
> 2008
> [87865.383613] secs since 1970: 1213303430, time:Thu Jun 12 20:43:50
> 2008
> [87925.263261] secs since 1970: 1213303490, time:Thu Jun 12 20:44:50
> 2008
> [87985.142794] secs since 1970: 1213303550, time:Thu Jun 12 20:45:50
> 2008
> [88045.022465] secs since 1970: 1213303610, time:Thu Jun 12 20:46:50
> 2008
> [88104.901993] secs since 1970: 1213303670, time:Thu Jun 12 20:47:50
> 2008
> [88164.781555] secs since 1970: 1213303730, time:Thu Jun 12 20:48:50
> 2008
> [88224.661193] secs since 1970: 1213303790, time:Thu Jun 12 20:49:50
> 2008
> [88284.540777] secs since 1970: 1213303850, time:Thu Jun 12 20:50:50
> 2008
> [88344.420448] secs since 1970: 1213303910, time:Thu Jun 12 20:51:50
> 2008
> [88404.299957] secs since 1970: 1213303970, time:Thu Jun 12 20:52:50
> 2008
> [88464.179722] secs since 1970: 1213304030, time:Thu Jun 12 20:53:50
> 2008
> [88524.059229] secs since 1970: 1213304090, time:Thu Jun 12 20:54:50
> 2008
> [88583.938799] secs since 1970: 1213304150, time:Thu Jun 12 20:55:50
> 2008
> [88643.818430] secs since 1970: 1213304210, time:Thu Jun 12 20:56:50
> 2008
> [88703.698102] secs since 1970: 1213304270, time:Thu Jun 12 20:57:50
> 2008
> [88763.577552] secs since 1970: 1213304330, time:Thu Jun 12 20:58:50
> 2008
> [88823.457180] secs since 1970: 1213304390, time:Thu Jun 12 20:59:50
> 2008
> [88883.336805] secs since 1970: 1213304450, time:Thu Jun 12 21:00:50
> 2008
> [88943.216354] secs since 1970: 1213304510, time:Thu Jun 12 21:01:50
> 2008
> [89003.095940] secs since 1970: 1213304570, time:Thu Jun 12 21:02:50
> 2008
> [89062.975550] secs since 1970: 1213304630, time:Thu Jun 12 21:03:50
> 2008
> [89122.855184] secs since 1970: 1213304690, time:Thu Jun 12 21:04:50
> 2008
> [89182.734796] secs since 1970: 1213304750, time:Thu Jun 12 21:05:50
> 2008
> [89242.614451] secs since 1970: 1213304810, time:Thu Jun 12 21:06:50
> 2008
> [89302.494083] secs since 1970: 1213304870, time:Thu Jun 12 21:07:50
> 2008
> [89362.373748] secs since 1970: 1213304930, time:Thu Jun 12 21:08:50
> 2008
> [89422.253149] secs since 1970: 1213304990, time:Thu Jun 12 21:09:50
> 2008
> [89482.132723] secs since 1970: 1213305050, time:Thu Jun 12 21:10:50
> 2008
> [89542.012413] secs since 1970: 1213305110, time:Thu Jun 12 21:11:50
> 2008
> [89601.892321] secs since 1970: 1213305171, time:Thu Jun 12 21:12:51
> 2008
> [89661.771534] secs since 1970: 1213305231, time:Thu Jun 12 21:13:51
> 2008
> [89721.651093] secs since 1970: 1213305291, time:Thu Jun 12 21:14:51
> 2008
> [89781.530707] secs since 1970: 1213305351, time:Thu Jun 12 21:15:51
> 2008
> [89841.410355] secs since 1970: 1213305411, time:Thu Jun 12 21:16:51
> 2008
> [89901.289916] secs since 1970: 1213305471, time:Thu Jun 12 21:17:51
> 2008
> [89961.169452] secs since 1970: 1213305531, time:Thu Jun 12 21:18:51
> 2008
> [90021.049277] secs since 1970: 1213305591, time:Thu Jun 12 21:19:51
> 2008
> [90080.928731] secs since 1970: 1213305651, time:Thu Jun 12 21:20:51
> 2008
> [90140.808362] secs since 1970: 1213305711, time:Thu Jun 12 21:21:51
> 2008
> [90200.687903] secs since 1970: 1213305771, time:Thu Jun 12 21:22:51
> 2008
> [90260.567678] secs since 1970: 1213305831, time:Thu Jun 12 21:23:51
> 2008
> [90320.447062] secs since 1970: 1213305891, time:Thu Jun 12 21:24:51
> 2008
> [90380.326679] secs since 1970: 1213305951, time:Thu Jun 12 21:25:51
> 2008
> [90440.206252] secs since 1970: 1213306011, time:Thu Jun 12 21:26:51
> 2008
> [90500.085917] secs since 1970: 1213306071, time:Thu Jun 12 21:27:51
> 2008
> [90559.965484] secs since 1970: 1213306131, time:Thu Jun 12 21:28:51
> 2008
> [90619.845052] secs since 1970: 1213306191, time:Thu Jun 12 21:29:51
> 2008
> [90679.724900] secs since 1970: 1213306251, time:Thu Jun 12 21:30:51
> 2008
> [90739.604366] secs since 1970: 1213306311, time:Thu Jun 12 21:31:51
> 2008
> [90799.483803] secs since 1970: 1213306371, time:Thu Jun 12 21:32:51
> 2008
> [90859.363649] secs since 1970: 1213306431, time:Thu Jun 12 21:33:51
> 2008
> [90919.243037] secs since 1970: 1213306491, time:Thu Jun 12 21:34:51
> 2008
> [90979.122646] secs since 1970: 1213306551, time:Thu Jun 12 21:35:51
> 2008
> [91039.002174] secs since 1970: 1213306611, time:Thu Jun 12 21:36:51
> 2008
> [91098.881855] secs since 1970: 1213306671, time:Thu Jun 12 21:37:51
> 2008
> [91158.761414] secs since 1970: 1213306731, time:Thu Jun 12 21:38:51
> 2008
>
>
> Roger Cruz
> Principal SW Engineer
> Marathon Technologies Corp.
> 978-489-1153
>
>
>
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