On Wed, Jul 23, 2014 at 10:25:34PM +0100, Mark Salter wrote: > On Fri, 2014-07-11 at 13:45 +0100, Catalin Marinas wrote: > > On Fri, Jul 11, 2014 at 02:26:48AM +0100, Laura Abbott wrote: > > > Mark Salter actually proposed a fix to this back in May > > > > > > https://lkml.org/lkml/2014/5/2/311 > > > > > > I never saw any further comments on it though. It also matches what x86 > > > does with their TLB flushing. It fixes the problem for me and the threshold > > > seems to be the best we can do unless we want to introduce options per > > > platform. It will need to be rebased to the latest tree though. > > > > There were other patches in this area and I forgot about this. The > > problem is that the ARM architecture does not define the actual > > micro-architectural implementation of the TLBs (and it shouldn't), so > > there is no way to guess how many TLB entries there are. It's not an > > easy figure to get either since there are multiple levels of caching for > > the TLBs. > > > > So we either guess some value here (we may not always be optimal) or we > > put some time bound (e.g. based on sched_clock()) on how long to loop. > > The latter is not optimal either, the only aim being to avoid > > soft-lockups. > > Sorry for the late reply... > > So, what would you like to see wrt this, Catalin? A reworked patch based > on time? IMO, something based on loop count or time seems better than > the status quo of a CPU potentially wasting 10s of seconds flushing the > tlb. I think we could go with a loop for simplicity but with a larger number of iterations only to avoid the lock-up (e.g. 1024, this would be 4MB range). My concern is that for a few global mappings that may or may not be in the TLB we nuke both the L1 and L2 TLBs (the latter can have over 1K entries). As for optimisation, I think we should look at the original code generating such big ranges. Would you mind posting a patch against the latest kernel? -- Catalin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>