On Mon, 2013-09-30 at 12:29 -0700, Linus Torvalds wrote: > > But I'm cc'ing the POWER people, because I don't know the POWER8 > interfaces, and I don't want to necessarily call this "xbegin"/"xend" > when I actually wrap it in some helper functions. The main problem with powerpc TM is that we need to handle interrupts happening while in transactional state. We currently only handle that for userspace. Mikey, how hard would it be to detect the in-kernel TM case and just simulate an abort in the exception entry ? (return to tbegin basically) Transactions in kernel make me nervous because of the PC jumping around on aborts and how easy we can get that stuff wrong :-) They also have interesting ordering semantics vs. locks, we need to be a tad careful (as long as we don't access a lock variable transactionally we should be ok. If we do, then spin_unlock needs a stronger barrier). The basic semantic for us is tbegin. [...] tend instructions. If the transaction fails, control returns to tbegin. (can happen at any point) which returns a CC code indicating success or failure. Things get really complicated if you take an interrupt however, the transaction gets into some special "suspended" state, it doesn't just die so we need to handle things in our interrupt entry (even if it's just to make the transaction abort cleanly) and right now we don't when coming from kernel space. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
