* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Fri, May 31, 2013 at 08:09:17AM +0400, Max Filippov wrote: > > Hi Peter, > > > > On Wed, May 29, 2013 at 9:51 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > What about something like this? > > > > With that patch I still get mtest05 firing my TLB/PTE incoherency > > check in the UP PREEMPT_VOLUNTARY configuration. This happens after > > zap_pte_range completion in the end of unmap_region because of > > rescheduling called in the following call chain: > > OK, so there two options; completely kill off fast-mode or something > like the below where we add magic to the scheduler :/ > > I'm aware people might object to something like the below -- but since > its a possibility I thought we ought to at least mention it. > > For those new to the thread; the problem is that since the introduction > of preemptible mmu_gather the traditional UP fast-mode is broken. > Fast-mode is where we free the pages first and flush TLBs later. This is > not a problem if there's no concurrency, but obviously if you can > preempt there now is. > > I think I prefer completely killing off fast-mode esp. since UP seems to > go the way of the Dodo and it does away with an exception in the > mmu_gather code. > > Anyway; opinions? Linus, Thomas, Ingo? Since UP kernels have not been packaged up by major distros for years, and since the live-patching of SMP kernels (the SMP alternative-instructions patching machinery) does away with a big chunk of the SMP cost, I guess UP kernels are slowly becoming like TINY_RCU: interesting but not really a primary design goal? ( Another reason for reducing SMP vs. UP complexity in this area would be the fact that we had a few bad regressions lately - the TLB code is not getting simpler, and bugs are getting discovered and fixed slower. ) At least that's the x86 perspective. ARM might still see it differently? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
