Nailed it down to recv(...) function call. Measured with 1 µs resolution this call usually take around 1 µs but sometimes it take up several thousand micro seconds. Previously measured these delays of several milliseconds seems to happen with a periodicity of 16 to 17 milliseconds corresponding to a frequency of around 60 Hz. Rule out noise from power grid since this is 50 Hz in Sweden.
Have not had time to try what you suggest yet but have a lot more time tommorow. Anybody have any about cause of these extra delays on recv(...) ?? Rule blocking call since data i sent in an Ethercat ring from a single thread. With no Ethernet frames sent it should either block or receive. 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
