Re: big picture UDP/IP performance question re 2.6.18 -> 2.6.32

From: starlight
Date: Thu Oct 06 2011 - 23:33:34 EST

After writing the last post, the large
difference in IRQ rate between the older
and newer kernels caught my eye.

I wonder if the hugely lower rate in the older
kernels reflects a more agile shifting
into and out of NAPI mode by the network

In this test the sending system
pulses data out on millisecond boundaries
due to the behavior of nsleep(), which
is used to establish the playback pace.

If the older kernels are switching to NAPI
for much of surge and the switching out
once the pulse falls off, it might
conceivably result in much better latency
and overall performance.

All tests were run with Intel 82571
network interfaces and the 'e1000e'
device driver. Some used the driver
packaged with the kernel, some used
Intel driver compiled from the source
found on Never could
detected any difference between the two.

Since data in the production environment
also tends to arrive in bursts, I don't find
the pulsing playback behavior a detriment.

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