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Receive side scaling.. crap?

post #1 of 3
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Pretty simple explanation of what rss does, scales the load across multiple cores to allow higher throughput, well.. can anyone explain why when using netperf to push as much bandwidth as the nic/cables/router can take (gigabit network), i get 8% HIGHER cpu utilization & 5-10mbps LESS throughput (plus some throughput jitter) with rss on compared to off? Off is giving LESS cpu utilization with MORE throughput, is between my sig systems laptop/desktop, the trend continues even with both cpus clocked well under stock, both have the latest nic drivers installed, same nic buffer & offload settings with all power saving green ethernet etc, off.
     
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Core i7 6700k @ 4.5 GHz Asus Sabertooth Z170 S ZOTAC GTX 1070 AMP! 8GB G.SKILL Ripjaws V 16GB DDR4 2400 @ 2800 
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post #2 of 3
Probably additional overhead and/or latency juggling threads, although I'm not that familiar with the function.

Even something like an Athlon II 260u @ 800 MHz doesn't have an issue pumping enough traffic through gigabit (ie my server) if your storage is capable enough.
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post #3 of 3
The goal of scaling isn't necessarily lower CPU utilization it is lower latency and higher throughput (and possibly more balanced CPU utilization). When you involve more cores there is more contention for shared resources so efficiency can be lower.

You should also be aware that a single TCP connection will normally not be parallelized across multiple cores. To really see the benefit of RSS you have to have multiple connections sending out many small packets with nagles algorithm disabled.
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