On Fri, 2 Mar 2007, Ingo Molnar wrote: > > * Davide Libenzi <davidel@xmailserver.org> wrote: > > > [...] We're still missing proper FPU context switch in the > > move_user_context(). [...] > > yeah - i'm starting to be of the opinion that the FPU context should > stay with the threadlet, exclusively. I.e. when calling a threadlet, the > 'outer loop' (the event loop) should not leak FPU context into the > threadlet and then expect it to be replicated from whatever random point > the threadlet ended up sleeping at. It would be possible, but it just > makes no sense. What makes most sense is to just keep the FPU context > with the threadlet, and to let the 'new head' use an initial (unused) > FPU context. And it's in fact the threadlet that will most likely have > an acrive FPU context across a system call, not the outer loop. In other > words: no special FPU support needed at all for threadlets (i.e. no > flipping needed even) - this behavior just naturally happens in the > current implementation. Hm?
I think that the "dirty" FPU context must, at least, follow the new head. That's what the userspace sees, and you don't want an async_exec to re-emerge with a different FPU context. I think it should also follow the async thread (old, going-to-sleep, thread), since a threadlet might have that dirtied, and as a consequence it'll want to find it back when it's re-scheduled. So, IMO, if the USEDFPU bit is set, we need to sync the dirty FPU context with an early unlazy_fpu(), *and* copy the sync'd FPU context to the new head. This should really be a fork of the dirty FPU context IMO, and should only happen if the USEDFPU bit is set. - Davide - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
