[PATCH v3 0/2] allow creating thread with real-time priority

[Morten Brørup]

> From: Thomas Monjalon [mailto:thomas at monjalon.net]
> Sent: Thursday, 26 October 2023 16.05
> 
> 26/10/2023 15:57, Morten Brørup:
> > > From: Morten Brørup [mailto:mb at smartsharesystems.com]
> > > Sent: Thursday, 26 October 2023 15.45
> > >
> > > > From: Thomas Monjalon [mailto:thomas at 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".
> > 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.)
> 
> 10 ms looks like an eternity.

Agree. It is only for functional testing, not for production!

> I will try.
> (Anyway I did a mistake when sending v4)
> 
>