Hi, On Wed, Jun 24, 2020 at 10:55 AM Joel Fernandes <joe...@google.com> wrote: > > On Wed, Jun 24, 2020 at 1:52 PM Qais Yousef <qais.you...@arm.com> wrote: > > > > On 06/24/20 13:35, Joel Fernandes wrote: > > > > [...] > > > > > > Doing the in-kernel opt-out via API should be fine, I think. But this > > > > will > > > > need to be discussed in the wider circle. It will already clash with > > > > this for > > > > example > > > > > > > > https://lore.kernel.org/lkml/20200619172011.5810-1-qais.you...@arm.com/ > > > > > > Have not yet looked closer at that patch, but are you saying this > > > patch clashes with that work? Sorry I am operating on 2 hours of sleep > > > here. > > > > The series is an optimization to remove the uclamp overhead from the > > scheduler > > fastpath until the userspace uses it. It introduces a static key that is > > disabled by default and will cause uclamp logic not to execute in the fast > > path. Once the userspace starts using util clamp, which we detect by either > > > > 1. Changing uclamp value of a task with sched_setattr() > > 2. Modifying the default sysctl_sched_util_clamp_{min, max} > > 3. Modifying the default cpu.uclamp.{min, max} value in cgroup > > > > If we start having in-kernel users changing uclamp value this means drivers > > will cause the system to opt-in into uclamp automatically even if the > > userspace doesn't actually use it. > > > > I think we can solve this by providing a special API to opt-out safely. > > Which > > is the right thing to do anyway even if we didn't have this clash. > > Makes sense, thanks.
OK, so I think the summary is: 1. There are enough external dependencies that are currently in the works that it makes sense for those to land first without trying to cram my patch to cros_ec in. 2. Maybe, as part of the work that's already going on, someone will add an API that I can use. If so then I can write my patch once that lands. 3. If nobody adds an API then I could look at adding the API myself once everything else is settled. 4. It looks as if the patch you mentioned originally [1] that allows userspace to just fully disable uclamp for RT tasks will land eventually (if we're stuck for a short term solution we can pick the existing patch). I believe Chrome OS will use that to just fully disable the default boosting for RT tasks across our system and (if needed) add boosts on a case-by-case basis. Once we do that, the incentive to land a patch for cros_ec will be mostly gone and probably we could consider my patch abandoned. While it would technically still be sane to land it won't have any real-world benefit. [1] https://lore.kernel.org/r/20200511154053.7822-1-qais.you...@arm.com
