On Thu, Nov 19, 2020 at 09:23:47AM -0800, Linus Torvalds wrote: > On Thu, Nov 19, 2020 at 3:14 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > I still hate all of this, and I really fear that with migrate_disable() > > available, people will be lazy and usage will increase :/ > > > > Case at hand is this series, the only reason we need it here is because > > per-cpu page-tables are expensive... > > No, I think you as a scheduler person just need to accept it. Well, I did do write the patches. > Because this is certainly not the only time migration limiting has > come up, and no, it has absolutely nothing to do with per-cpu page > tables being completely unacceptable. It is for this instance; but sure, it's come up before in other contexts. > The scheduler people need to get used to this. Really. Because ASMP is > just going to be a fact. ASMP is different in that it is a hardware constraint, you're just not going to be able to run more of X than there's X capable hardware units on (be if FPUs, Vector units, 32bit or whatever) > There are few things more futile than railing against reality, Peter. But, but, my windmills! :-) > Honestly, the only argument I've ever heard against limiting migration > is the whole "our scheduling theory doesn't cover it". > > So either throw the broken theory away, or live with it. Theory that > doesn't match reality isn't theory, it's religion. The first stage of throwing it out is understanding the problem, which is just about where we're at. Next is creating a new formalism (if possible) that covers this new issue. That might take a while. Thing is though; without a formalism to reason about timeliness guarantees, there is no Real-Time. So sure, I've written the patches, doesn't mean I have to like the place we're in due to it.
