Re: [RFC} Commit 8a99b6833c88 Moves Important Real-time Settings To DebugFS

[Joseph Salisbury]

On 8/18/22 21:38, Joseph Salisbury wrote:
> On 8/18/22 16:31, Peter Zijlstra wrote:
> > On Thu, Aug 18, 2022 at 03:53:28PM -0400, Joseph Salisbury wrote:
> > > Hello,
> > >
> > > Some Ubuntu users are using the tuned package with a 5.15.x based 
> > > real-time
> > > kernel.  Tuned adjusts various sysctl options based on a specified 
> > > profile.
> > > This userspace package has stopped working > 5.13 due to the following
> > > commit:
> > >
> > > 8a99b6833c88 "(sched: Move SCHED_DEBUG sysctl to debugfs)"
> > >
> > > This commit moved some important real-time sysctl knobs to debugfs in
> > > 5.13-rc1.  It also appears some of the sysctl options were not moved,
> > > sched_min_granularity_ns, for example.
> > >
> > > I was hoping to get some feedback on how to approach this. Would 
> > > upstream
> > > real-time consider accepting a patch to the 5.15 real-time patch set 
> > > that
> > > reverts this commit?  Or a new patch that adds the sysctl settings 
> > > back?
> > > Any other ideas or feedback would be appreciated!
> > None of those knobs were available when SCHED_DEBUG=n, so relying on
> > them is your error to begin with.
> We have had SCHED_DEBUG=y while this kernel is in beta, so you are 
> correct.  I need to investigate a different approach.
> > Secondly, real-time? Which if those values affects anything in
> > SCHED_FIFO/RR/DEADLINE ?
> I am in the process of understanding how tuned[0] works. Many users 
> have reported success using tuned.  One use case for tuned is to 
> assign isolated cores to real-time processes and then move managed 
> IRQs out of these isolated cores.  This can be done easily with tuned 
> (I will research if there are other options to suggest). However, 
> tuned is trying to set the affected values when enabling a profile, 
> such as the real-time profile (Tuned offers many profiles based on a 
> workload type).
>
> I will investigate further to answer your point of what in 
> SCHED_FIFO/RR/DEADLINE those values affect.  It could be those values 
> are not needed at all. The dependency on them might be left over from 
> some need that no longer exists.
>
> Thank you again for the feedback!
>
> [0] https://tuned-project.org/
I also see that the github repo[0] is at version 2.19-rc1, and the 
version being testing is 2.15.  Many of the issues we see may already be 
resolved.

I will find out how I can participate in the tuned community.  At a 
minimum, I can start with testing and bug fixes.

Thanks again for your feedback, Peter.  And sorry for the noise.

Thanks,

Joe

[0] https://github.com/redhat-performance/tuned