latency calculation has potential performance issues

https://bugs.dpdk.org/show_bug.cgi?id=385

            Bug ID: 385
           Summary: latency calculation has potential performance issues
           Product: DPDK
           Version: 19.11
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: minor
          Priority: Normal
         Component: other
          Assignee: [email protected]
          Reporter: [email protected]

Target Milestone: ---

If anyone is using rte_latencystats, they are in for a big performance hit.

The code in rte_latencystats uses a receive and transmit callback for each burst. The latency calculation is using floating point (slow) and worse yet there is several floating point divides per packet. A floating point divide is one of the slowest opcodes on any processor.

The code should be changed to keep track of cycles (fixed point 64 bit) and convert the result to floating point when doing update. Or better yet only use fixed point maths.

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