Re: [LibreQoS] Fwd: [PATCH net-next 0/4] tsnep: Throttle irq, rotten pkts, RX buffer alloc and ethtool_get_channels()

[Gerhard Engleder <gerhard@engleder-embedded.com>]

On 17.11.22 22:02, Dave Taht wrote:
> time sensitive networking is a thing. Now less sensitive. At least on
> this a53, an interrupt rate of 20us resulted in total cpu usage at a
> gbit...
> 
> Taking a 7x hit in latency tho, to reduce the cpu load, strikes me as
> a lot. dpdk would just spin-read here, vs a vs xdp.

7x less interrupts does not mean that latency is also 7x higher, but
latency will definitely be increased. A balance between CPU load and
latency need to be found here.

> "Without interrupt throttling, iperf server mode generates a CPU load of
> 100% (A53 1.2GHz). Also the throughput suffers with less than 900Mbit/s
> on a 1Gbit/s link. The reason is a high interrupt load with interrupts
> every ~20us.
> 
> Reduce interrupt load by throttling of interrupts. Interrupt delay is
> configured statically to 64us. For iperf server mode the CPU load is
> significantly reduced to ~20% and the throughput reaches the maximum of
> 941MBit/s. Interrupts are generated every ~140us."