Nick Piggin writes: > > I just wish we had even one actual example of things going wrong with > > the current rules we have on powerpc to motivate changing to this > > model. > > ~/usr/src/linux-2.6> git grep test_and_set_bit drivers/ | wc -l > 506 > How sure are you that none of those forms part of a cobbled-together > locking scheme that hopes to constrain some IO access?
My comment was precisely about the fact that this sort of argument is actually FUD. I want one example that is demonstrably wrong, not just a "how sure are you". > But surely you have to audit the drivers anyway to ensure they are OK > with the current powerpc scheme. In which case, once you have audited > them and know they are safe, you can easily convert them to the even > _faster_ __readl/__writel, and just add the appropriate barriers. The trouble is that as code gets maintained, using __writel + explicit barriers is more fragile because some people will change the code, or add new code, without understanding the barriers. So whenever a driver gets converted to using __writel + barriers, we will end up having to watch every change that goes into it forever. Whereas with the current scheme there's a much smaller set of gotchas to watch out for, and the gotchas are things that already raise red flags, such as open-coded locking and any sort of "clever" lockless scheme. Paul. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
