On Mon, Apr 26, 2021 at 5:12 PM Andrew Lutomirski <luto(a)mit.edu> wrote:
On Mon, Apr 26, 2021 at 1:29 PM Justin Forbes <jmforbes(a)linuxtx.org> wrote:
>
> On Mon, Apr 26, 2021 at 11:25 AM Vitaly Zaitsev via devel
> <devel(a)lists.fedoraproject.org> wrote:
> >
> > On 25.04.2021 20:39, Artem Tim wrote:
> > > Please provide full PREEMPT mode by default in 5.12 kernel for desktop
variants. With 5.12 it is possible for user to change it without efforts if they need
this.
> >
> > +1 for this. Significantly reduces X11 input lag in full-screen games.
> >
>
> From a kernel standpoint, I do not think turning on CONFIG_PREEMPT is
> desired. That sets the *default* to PREEMPT, and changes the current
> situation. I plan to keep CONFIG_PREEMPT_VOLUNTARY as the default.
I'm curious: why do you prefer voluntary as the default instead of full preempt?
It has always been a nice balance for Fedora where we do have a lot of
desktop users, but also a lot of server users. And it has been well
tested as the Fedora default for quite some time, and the default for
RHEL as well. I don't specifically dislike the full preempt, but
introducing such a change to rebases on release Fedora is a risk I
don't think we should take. I might be willing to make such a change
for Fedora 35, where we have plenty of time to test on various
workloads, but that doesn't help anyone for a good 6 months. I would
much rather get the option for users now (I will even put the patch in
5.12 if I know it is headed upstream).
> The
> code introduced is odd, in that you can choose other options (none,
> voluntary, full) based on that starting point, but it doesn't allow
> you to default to anything else and keep CONFIG_PREEMPT_DYNAMIC on to
> choose more preemption than the default.
I've pinged the right people. I'll try to make this happen.
Thanks. If not I can take a look. The code looks good, it is just an
unfortunate lack of options for distros who would like to use dynamic
without disrupting defaults.
Justin