On Thu, May 25, 2017 at 5:31 AM, Michel Dänzer <michel at daenzer.net> wrote: > On 24/05/17 08:27 PM, Christian König wrote: >> Am 24.05.2017 um 13:03 schrieb Marek Olšák: >>>> >>> I think the final solution (done in fault_reserve_notify) should be: >>> if (bo->num_cpu_page_faults++ > 20) >>> bo->preferred_domain = GTT_WC; > > I agree something like that will probably be part of the solution, but I > doubt it's quite that simple or that it's the only thing that can be > improved. > > >> I more or less agree on that, but setting preferred_domain permanently >> to GTT_WC is what worries me a bit. >> >> E.g. imagine you alt+tab from a game to your browser and back and the >> game runs way slower now because BOs are never moved back to VRAM. > > Right, permanently moving a BO to GTT might itself cause performance to > drop down a cliff in some cases. It's possible that this is irrelevant > compared to excessive buffer migration for CPU access though. > > >> What we need is a global limit of number of bytes transfered per second >> for swap operations or something like that. >> >> Or maybe a timeout which says when a BO was moved (either by swapping it >> out or by a CPU page fault) only move it back after +n jiffies or >> something like that. > > I also feel like something like this will be more useful than the number > of CPU page faults per se. But I'm curious what Marek comes up with. :) I don't have any better idea at the moment. It looks like John Brooks has already solved this issue based on his IRC comments. Marek
