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[Xen-API] delays with network traffic

To: xen-api@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-API] delays with network traffic
From: George Shuklin <george.shuklin@xxxxxxxxx>
Date: Mon, 25 Apr 2011 19:31:20 +0400
Delivery-date: Mon, 25 Apr 2011 08:31:41 -0700
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Good day.

Found strange behavior with xapi and guest network traffic. If we starts
to ping domU with high speed (about 3-4 pings per second) and do some
operations with xapi (f.e. xe vm-list, etc) we can see delays in pings
(up to 80 ms compare to usual 0.3-0.8). All guest are PVs.

I dig pretty much about this and found:

1) raising nice number for xenstored (nice 10, nice 20) make delays
2) Pinning dom0 and adding VCPU to dom0 slightly helps, but not
3) switching to bridge instead ovs makes things worse (but not really
4) CPU load in domU does not change behavior (not better, not worse)
5) High network and disk activity for domU make it replays sometimes
longer (up to 100ms with average load < 0.5)

In some tests I was able to get ping about 5-6ms instead 0.3-0.8 just by
running python (without options).

I feel I miss something or do not understand.

wBR, George.

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