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gaps in waterfalls
10-09-2012, 08:54 PM
Post: #1
gaps in waterfalls
Hi Pat,

we have trouble with some own agents, version 2.7. They are running on virtual machines (win 7). Some are virtualized via XEN and some via KVM. The Problem is that we have gaps in waterfalls where browser seems to do nothing (see attached har). The gaps doesn't appear in all measurements, but around every 15th measurement is affected.
We identified high-precision-timer of kvm-/xen-host as source of trouble: the host sends very much timer-interrupts to win-vm's. Apparently windows can't handle all of these in time and so regularly puts the local clock forward. Deactivating high-precision-timer seems to solve the problem or even leads to smaller gaps in waterfall (what still isn't optimal).

Ever observed similar behaviour?

Regards Nils


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.zip  www.otto.de.121004_07_a6c2beaeb77716e05f2b80864695faa2.har.zip (Size: 35.35 KB / Downloads: 58)
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10-09-2012, 10:18 PM
Post: #2
RE: gaps in waterfalls
Yes, I have seen it with KVM but Xen generally performs better. You can sometimes make it better by using /USEPMTIMER in boot.ini (XP/2003) or BCEDIT on Windows 7.

I haven't seen the problem with VMWare which is one of the reasons I use it for most of my VM's.
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