Messages in this thread | | | Date | Thu, 06 Oct 2011 23:27:35 -0400 | From | starlight@binnacle ... | Subject | Re: big picture UDP/IP performance question re 2.6.18 -> 2.6.32 |
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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 bottom-half.
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 sourceforge.net. 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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