On Thu, Nov 22, 2018 at 03:59:50PM +0200, Joonas Lahtinen wrote: > Hi Jerome, > > Bit late reply, but here goes :) > > We're working quite hard to avoid pinning any pages unless they're in > the GPU page tables. And when they are in the GPU page tables, they must > be pinned for whole of that duration, for the reason that our GPUs can > not take a fault. And to avoid thrashing GPU page tables, we do leave > objects in page tables with the expectation that smart userspace > recycles buffers. > > So what I understand of your proposal, it wouldn't really make a > difference for us in the amount of pinned pages (which I agree, > we'd love to see going down). When we're unable to take a fault, > the first use effectively forces us to pin any pages and keep them > pinned to avoid thrashing GPU page tables. > > So from i915 perspective, it just seems to be mostly an exchange of > an API to an another for getting the pages. You already mentioned > the fast path is being worked on, which is an obvious difference. > But is there some other improvement one would be expecting, beyond > the page pinning? > > Also, is the requirement for a single non-file-backed VMA in the > plans of being eliminated or is that inherent restriction of the > HMM_MIRROR feature? We're currently not imposing such a limitation. I think a clear plus for HMM would be if this helps us fix the deadlocks and races we're seeing. But I have no idea whether this gets us any closer here or not. -Daniel > > Regards, Joonas > > Quoting jglisse@xxxxxxxxxx (2018-09-10 03:57:36) > > From: Jérôme Glisse <jglisse@xxxxxxxxxx> > > > > This replace existing code that rely on get_user_page() aka GUP with > > code that now use HMM mirror to mirror a range of virtual address as > > a buffer object accessible by the GPU. There is no functional changes > > from userspace point of view. > > > > From kernel point of view we no longer pin pages for userptr buffer > > object which is a welcome change (i am assuming that everyone dislike > > page pin as i do). > > > > Another change, from kernel point of view, is that it does no longer > > have a fast path with get_user_pages_fast() this can eventually added > > back through HMM. > > > > Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx> > > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx > > Cc: David Airlie <airlied@xxxxxxxx> > > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Cc: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx> > > Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> > > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> > > Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx> > > Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
