[Intel-gfx] [PATCH] extend prefault helpers to fault in more than PAGE_SIZE
daniel.vetter at ffwll.ch
Thu Feb 16 13:01:35 CET 2012
drm/i915 has write/read paths to upload/download data to/from gpu buffer
objects. For a bunch of reasons we have special fastpaths with decent setup
costs, so when we fall back to the slow-path we don't fully recover to the
fastest fast-path when grabbing our locks again. This is also in parts due to
that we have multiple fallbacks to slower paths, so control-flow in our code
would get really ugly.
As part of a larger rewrite and re-tuning of these functions we've noticed that
the prefault helpers in pagemap.h only prefault up to PAGE_SIZE because that's
all the other users need. The follow-up patch extends this to abritary sizes so
that we can fully exploit our special fastpaths in more cases (we typically see
reads and writes of a few pages up to a few mb).
I'd like to get this in for 3.4. There's no functional dependency between this
patch and the drm/i915 rework (only performance effects), so this can go in
through -mm without causing merge issues.
If this or something similar isn't acceptable, plan B is to hand-roll these 2
functions in drm/i915. But I don't like nih these things in driver code much.
Comments highly welcome.
For reference, the drm/i915 read/write rework is avaialable at:
Unfortunately cgit.fd.o is currently on hiatus.
Daniel Vetter (1):
mm: extend prefault helpers to fault in more than PAGE_SIZE
include/linux/pagemap.h | 28 ++++++++++++++++++----------
1 files changed, 18 insertions(+), 10 deletions(-)
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