On Thu, Oct 26, 2023 at 3:57 PM Morten Brørup <m...@smartsharesystems.com> wrote: > > > From: Morten Brørup [mailto:m...@smartsharesystems.com] > > Sent: Thursday, 26 October 2023 15.45 > > > > > From: Thomas Monjalon [mailto:tho...@monjalon.net] > > > Sent: Thursday, 26 October 2023 15.37 > > > > > > 25/10/2023 18:31, Thomas Monjalon: > > > > Real-time thread priority was been forbidden on Unix > > > > because of problems they can cause. > > > > Warnings and helpers are added to avoid deadlocks, > > > > so real-time can be allowed on all systems. > > > > > > Unit test is failing: > > > DPDK:fast-tests / threads_autotest TIMEOUT 600.01 s > > > > > > It is seen in only 1 target (maybe the failure occurence is random): > > > Debian 11 (Buster) (ARM) | PASS > > > Fedora 37 (ARM) | PASS > > > CentOS Stream 9 (ARM) | FAIL > > > Fedora 38 (ARM) | PASS > > > Fedora 38 (ARM Clang) | PASS > > > Ubuntu 20.04 (ARM) | PASS > > > > > > I need to send a v4 with new implementation and better comments. > > > The Unix sleep will be upgraded from 1 ns to 1 us in case it makes a > > > difference. > > > > It will not make a difference. The kernel will go through the sleeping > > steps, > > then wake up again and see the real-time thread is ready to run, and then > > immediately schedule it. > > > > For testing purposes, consider sleeping 10 milliseconds or something > > significant like that. > > A bit more details... > > In our recent tests, nanosleep() itself took around 50 us. So you need to > sleep longer than that for your thread not to be runnable when the > nanosleep() wakes up again, because 50 us has already passed in "nanosleep > overhead".
You may want to read manual for prctl and look for PR_SET_TIMERSLACK. https://github.com/openvswitch/ovs/commit/f62629a55894546ff043e8a116c3c57aff73c285 > 10 milliseconds provides plenty of margin, and corresponds to 10 jiffies on a > 1000 Hz kernel. (I don't know if it makes any difference for the kernel > scheduler if the timer crosses a jiffy border or not.) -- David Marchand
