[LibreQoS] cpumap-pping 1.0 final

Herbert Wolverson herberticus at gmail.com
Tue Nov 15 09:08:29 EST 2022


Just wanted to announce that cpumap-pping is now tagged as the 1.0 release.

The one major change from RC1 is that the xdp_pping utility no longer does
any cleaning - it just reports statistics. That makes its execution a LOT
faster, and removes a stalling issue that was showing up under heavy (5
gbit/s+) load.

Under the hood, each "report flow" now carries a "recycle time" and a
"fresh data" flag. They are also stored in an "LRU map" rather than a
strict hash map - so if the buffer fills up, it automatically (in kernel
space) evicts (replaces) the oldest member rather than pausing to report
the event. This in turn allows for all memory allocation to be up-front (on
load), so there are *no* memory allocations or reallocations within the
running RTT tracking system.

Once a "report flow" has achieved its target number of samples, it stops
collecting data. 30 seconds (by default, it's configurable) later, the flow
is "recycled" - its buffer is empties, "fresh data" is set to false, and
the recycle time bumped to "now + 30 seconds". If data arrives, "fresh
data" is set to true - and the reporting tool will show the new data. If no
data arrives, the flow ages slowly to the bottom of the list and is
replaced with no memory allocation/deallocation/reallocation.

This has largely eliminated the occasional variance in execution time (it
never spiked above 6000 nanoseconds to begin with; but now it's
consistently under 0.0005 ms added ping time; you won't notice it). More
importantly, it completely eradicated the high-load behavior of the
xdp_pping sitting and spinning for long periods of times under high lock

-- Herbert
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