[Xen-devel] Puzzling ttcp behaviour on Xen

["Moffie, Micha" <micha.moffie@xxxxxx>]

We are running 2 ettcp (test TCP) tests on xen as follows:
Dom0 (source) to DomU (sink)
And
DomU (source) to Dom0 (sink)

Dom0 has 2 vcpus and 256MB of memory. 
DomU has 1 vcpu and 256MB of memory.

Results (in seconds) show that communications from DomU to Dom0 are
consistently
faster (we show first 3 tests):

(We are passing a 4KB block each time)
Source->Sink    # Transactions  tcp/ip I        tcp/ip II       tcp/ip
III             
Dom0 -> DomU    100000        4.77              4.76            4.79
dom0: -t
                        1000000         47.86           47.65
47.43           domU: -r
                        10000000                481.23  468.51  469.31

DomU -> Dom0    100000          1.81            1.89            1.79
domU: -t
                        1000000         17.19           17.23
16.98           dom0: -r
                        10000000                171.83  171.95  171.71




We observe the same behaviour when blocks are 8KB (default) or 640B
as well as when we use our inter domain communication channel 
(based on Xen rings, shared memory etc.)

Can anybody explain why?


Thanks so much,
:)
Micha.

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