[PATCH v3 0/7] dma-buf: Performance improvements for system heap & a system-uncached implementation

[John Stultz]

Hey All,
  So this is another revision of my patch series to performance
optimizations to the dma-buf system heap.

Unfortunately, in working these up, I realized the heap-helpers
infrastructure we tried to add to miniimize code duplication is
not as generic as we intended. For some heaps it makes sense to
deal with page lists, for other heaps it makes more sense to
track things with sgtables.

So this series reworks the system heap to use sgtables, and then
consolidates the pagelist method from the heap-helpers into the
CMA heap. After which the heap-helpers logic is removed (as it
is unused). I'd still like to find a better way to avoid some of
the logic duplication in implementing the entire dma_buf_ops
handlers per heap. But unfortunately that code is tied somewhat
to how the buffer's memory is tracked.

After this, the series introduces an optimization that
Ørjan Eide implemented for ION that avoids calling sync on
attachments that don't have a mapping.

Next, an optimization to use larger order pages for the system
heap. This change brings us closer to the current performance
of the ION code.

Unfortunately, after submitting the last round, I realized that
part of the reason the page-pooling patch I had included was
providing such great performance numbers, was because the
network page-pool implementation doesn't zero pages that it
pulls from the cache. This is very inappropriate for buffers we
pass to userland and was what gave it an unfair advantage
(almost constant time performance) relative to ION's allocation
performance numbers. I added some patches to zero the buffers
manually similar to how ION does it, but I found this resulted
in basically no performance improvement from the standard page
allocator. Thus I've dropped that patch in this series for now.

Unfortunately this means we still have a performance delta from
the ION system heap as measured by my microbenchmark, and this
delta comes from ION system_heap's use of deferred freeing of
pages. So less work is done in the measured interval of the
microbenchmark. I'll be looking at adding similar code
eventually but I don't want to hold the rest of the patches up
on this, as it is still a good improvement over the current
code.

I've updated the chart I shared earlier with current numbers
(including with the unsubmitted net pagepool implementation, and
with a different unsubmitted pagepool implementation borrowed
from ION) here:
https://docs.google.com/spreadsheets/d/1-1C8ZQpmkl_0DISkI6z4xelE08MlNAN7oEu34AnO4Ao/edit?usp=sharing

I did add to this series a reworked version of my uncached
system heap implementation I was submitting a few weeks back.
Since it duplicated a lot of the now reworked system heap code,
I realized it would be much simpler to add the functionality to
the system_heap implementaiton itself.

While not improving the core allocation performance, the
uncached heap allocations do result in *much* improved
performance on HiKey960 as it avoids a lot of flushing and
invalidating buffers that the cpu doesn't touch often.

Feedback on these would be great!

thanks
-john


New in v3:
* Dropped page-pool patches as after correcting the code to
  zero buffers, they provided no net performance gain.
* Added system-uncached implementation ontop of reworked
  system-heap.
* Use the new sgtable mapping functions, in the system and cma
  code  as Suggested-by: Daniel Mentz <danielmentz@xxxxxxxxxx>
* Cleanup: Use page_size() rather then open-coding it



Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Liam Mark <lmark@xxxxxxxxxxxxxx>
Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Brian Starkey <Brian.Starkey@xxxxxxx>
Cc: Hridya Valsaraju <hridya@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Sandeep Patil <sspatil@xxxxxxxxxx>
Cc: Daniel Mentz <danielmentz@xxxxxxxxxx>
Cc: Chris Goldsworthy <cgoldswo@xxxxxxxxxxxxxx>
Cc: Ørjan Eide <orjan.eide@xxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Cc: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
Cc: Simon Ser <contact@xxxxxxxxxxx>
Cc: James Jones <jajones@xxxxxxxxxx>
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx

John Stultz (7):
  dma-buf: system_heap: Rework system heap to use sgtables instead of
    pagelists
  dma-buf: heaps: Move heap-helper logic into the cma_heap
    implementation
  dma-buf: heaps: Remove heap-helpers code
  dma-buf: heaps: Skip sync if not mapped
  dma-buf: system_heap: Allocate higher order pages if available
  dma-buf: dma-heap: Keep track of the heap device struct
  dma-buf: system_heap: Add a system-uncached heap re-using the system
    heap

 drivers/dma-buf/dma-heap.c           |  33 +-
 drivers/dma-buf/heaps/Makefile       |   1 -
 drivers/dma-buf/heaps/cma_heap.c     | 327 +++++++++++++++---
 drivers/dma-buf/heaps/heap-helpers.c | 271 ---------------
 drivers/dma-buf/heaps/heap-helpers.h |  53 ---
 drivers/dma-buf/heaps/system_heap.c  | 480 ++++++++++++++++++++++++---
 include/linux/dma-heap.h             |   9 +
 7 files changed, 741 insertions(+), 433 deletions(-)
 delete mode 100644 drivers/dma-buf/heaps/heap-helpers.c
 delete mode 100644 drivers/dma-buf/heaps/heap-helpers.h

-- 
2.17.1