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Re: [Xen-devel] A clocksource question

To: Tobias Geiger <tobias.geiger@xxxxxxxxx>
Subject: Re: [Xen-devel] A clocksource question
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 12 Mar 2010 14:02:38 -0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Joanna Rutkowska <joanna@xxxxxxxxxxxxxxxxxxxxxx>
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On 03/12/2010 01:56 PM, Tobias Geiger wrote:
kbpc2:~# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
xen
kbpc2:~# cat
/sys/devices/system/clocksource/clocksource0/available_clocksource
xen
kbpc2:~# echo "jiffies"
/sys/devices/system/clocksource/clocksource0/current_clocksource
kbpc2:~# dmesg  | tail -1
[ 7898.642404] Override clocksource jiffies is not HRT compatible. Cannot switch
while in HRT/NOHZ mode
kbpc2:~#

Seems like it's not possible to switch to jiffies - however:
kbpc2:~# zcat /proc/config.gz | grep NO_HZ
# CONFIG_NO_HZ is not set

but CONFIG_SCHED_HRTICK=y

Interesting. BTW, does NO_HZ change the behaviour of this? In principle NO_HZ should be preferable, and particularly in a virtual machine since it should limit the number of timer interrupts.

Joanna, are you using NO_HZ?

Thanks,
    J

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