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From: Paul Emmerich <emmericp@net.in.tum.de>
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To: Stephen Hemminger <stephen@networkplumber.org>
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Subject: Re: [dpdk-dev] Polling too often at lower packet rates?
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Stephen Hemminger <stephen@networkplumber.org> wrote:

> Your excess polling consumes PCI bandwidth which is a fixed resource.

I doubt that this is the problem for three reasons:

* The poll rate would regulate itself if the PCIe bus was the bottleneck

* This problem only occurs with 82599 chips, not with X540 chips
 (which are virtually identical except for 10GBase-T vs. fiber)

* This effect already appears with relatively low poll rates (batch size 1).
 The overhead would have to be > 128 bytes per poll to saturate the PCIe bus
 at this rate. (Even if this was the case, my first point still applies)

I unfortunately don't have a test system with a CPU that supports PCIe
performance counters with a 82599 card. Otherwise I'd measure this since I
think this effect is really interesting (I'm a co-authors of the paper
linked above).


Paul