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[Xen-users] Resolution of jiffies Timer

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Resolution of jiffies Timer
From: Michael Renner <michael.renner@xxxxxxxxxxx>
Date: Tue, 29 Sep 2009 13:41:10 +0200
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I'm using Xen 3.2.1 with 2.6.26 as Dom0 and DomU in the x86_64 Versions/Builds as provided by Debian Lenny.

I noticed that when using "jiffies" as clocksource, the resolution of the timers in a DomU is 4ms, e.g. ping shows only runtimes in 4ms increments [1]. When using "xen" the resolution is fine (didn't make exact measurements) but xen is a no-go when migrating guests between Dom0s.

Is the 4ms resolution behavior expected or something specific to the Debian builds? Is there anything I can do to change the behavior?

Versions used:
xen-hypervisor-3.2-1-amd64          3.2.1-2
linux-image-2.6.26-2-xen-amd64          2.6.26-17lenny2

Relevant log messages:


(XEN) IOAPIC[0]: apic_id 8, version 32, address 0xfec00000, GSI 0-23
(XEN) IOAPIC[1]: apic_id 0, version 32, address 0xfec80000, GSI 24-47
(XEN) Enabling APIC mode:  Flat.  Using 2 I/O APICs
(XEN) Platform timer overflows in 14998 jiffies.
(XEN) Platform timer is 14.318MHz HPET


[    0.000000] IOAPIC[0]: apic_id 8, version 0, address 0xfec00000, GSI 0-23
[ 0.000000] IOAPIC[1]: apic_id 0, version 0, address 0xfec80000, GSI 24-47 [ 0.572038] Calibrating delay using timer specific routine.. 4801.61 BogoMIPS (lpj=9603225)


[ 0.968064] Calibrating delay using timer specific routine.. 4801.91 BogoMIPS (lpj=9603828)

best regards,
Michael Renner


64 bytes from www.example.com ( icmp_seq=4 ttl=51 time=172 ms 64 bytes from www.example.com ( icmp_seq=5 ttl=51 time=168 ms 64 bytes from www.example.com ( icmp_seq=6 ttl=51 time=176 ms 64 bytes from www.example.com ( icmp_seq=7 ttl=51 time=172 ms

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