Yes isolate the last CPU and pin the Ethernet IRQd to that CPU and pin other interrupts seems to do the trick. Running for six minutes worst delay of received packet is slightly above 153 µs.
If some other interrupt prevented receiving of ethernet frame it also agree with latency on receive I measured earlier. This is on the I350 card there I previously had delays of up to around 15 milliseconds followed by a burst of receives. If I could get the hardware time trigger to sending of frames then transmission would be perfect, equally spaced exactly at the intended, this is a small detail I do not however think make any difference in practice. Regard Nicklas Karlsson tor 2026-09-17 klockan 07:28 -0700 skrev Peter Wallace: > On Thu, 17 Sep 2026, andy pugh wrote: > > > On Wed, 16 Sept 2026 at 21:20, Nicklas SB Karlsson <[email protected]> wrote: > > > > > Running Linuxcnc and send receive Ethernet jitter is small for most > > > packets but sometimes there is delay of well > > > above on millisecond, running for maybe a minute or so worst case is > > > between 6...7 milliseconds. > > > > Maybe you need to disable IRQ coalescing? It's mentioned briefly in > > the hm2_eth docs, but also might be relevant to EtherCAT. > > https://linuxcnc.org/docs/stable/html/man/man9/hm2_eth.9.html > > > > (It's at least a google-able phrase for further investigation) > > At least for hm2_eth, basic Network latency improvement methods are: > > > On Intel (and some less common others like broadcom), disable IRQ coalescing > > On Realtek, install the DKMS driver (the stock Linux driver has multi-ms > random latencies) > > On all, use isolcpus (or whatever the newer scheme is called) to isolate the > last CPU, and then pin the Ethernet IRQ to that CPU. > > Use the latest kernel (I have a test system that always got random timeouts, > say once a day, with 6.x kernels, this was totally fixed with a 7.X kernel > > > > > > -- > > atp > > "A motorcycle is a bicycle with a pandemonium attachment and is > > designed for the especial use of mechanical geniuses, daredevils and > > lunatics." > > ? George Fitch, Atlanta Constitution Newspaper, 1912 > > > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > Peter Wallace > Mesa Electronics > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
