[Xen-API] delays with network traffic

[George Shuklin <george.shuklin@xxxxxxxxx>]

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
lower.
2) Pinning dom0 and adding VCPU to dom0 slightly helps, but not
significantly. 
3) switching to bridge instead ovs makes things worse (but not really
much).
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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