On Mon, Nov 29, 2010 at 6:53 PM, Kevin D. Kissell <kevink@xxxxxxxxxxxxx> wrote: > Having done surgery in the past to the ASID management code, this sounds > like > a much more rational explanation of the observed problem. Your proposed mod > sounds like it might work, but local_flush_tlb_mm() is implemented in terms > of > drop_mmu_context(), which only does what you want if the CPU executing the > code is *not* one of the CPUs participating in the memory map. Otherwise, > instead of clearing the ASID in the table, it allocates a new one. I have a > concern > that this may re-randomize things in a way that will solve your problem > *most* > of the time, but not always. > Actually, if you call this function late enough, specifically when cpu_online(cpu) is 0, it does exactly what I want from it - that is clears ASID in the context. I am calling it from play_dead() which is platform specific, but there might be a place for it in platform-independent code as well. Another option would be not to use drop_mmu_context() but rather clear the context directly, since we know exactly what we want to do at this point. > Now that we have a better understanding of the failure, your initial notion > of *not* restarting the ASID sequence on a hotplug insertion doesn't seem > as crazy - it's certainly the zen "doing by doing nothing" way to go, > without > the iterative overhead of walking the full process table. But as we > discussed, > it has the downside of requiring new state infrastructure for tracking > hotplugs, > and we'd want to be sure that it's well behaved in the case where we have a > post-initial-boot hotplug event that brings a CPU online that has never been > initialized. To take that tack, we'd need a per-CPU-slot bit which says "I > have > a valid ASID sequence, thank you", which is checked in per_cpu_trap_init() > (or some other appropriate hook), and the ASID "cache" is initialized only > if it's needed, which *might* be on a hotplug. You are talking about adding this bit to cpuinfo_mips, correct? Maksim. > > /K. >
