network IO buffer? -- Sisu

network IO buffer? -- Sisu

[Sisu Xi]

Hi, all:

I want to study the latency in receiving a pkt in Xen.
Here is my set up: kernel version is 2.6.32.25, applied the patch.
Credit Based Scheduler is used. Dom0 is with 1 VCPU, pinned to core 0,
while Dom1 and Dom2 (one VCPU each) are both pinned to another
separate core.

Then I run a echo program in Dom1 to another server. If there is no
interference, the round trip time was like 250 microseconds.
But, if I run a iperf in Dom2 to generate the maximum interference,
the round trip time in Dom1 was like 40 ms, 160 times the original
case!

Does anyone know where is the pkt buffered? I already checked the
net_rx_action in netback.c in Dom0, the length of the queue is like 1
or 2 most of the time, which meas the pkt is buffered some where else?

Could anyone help me with this?

Thanks very much!

Best!

Yours,
Sisu