[v2,0/5] fbdev: Improve performance of fbdev console

Message

Thomas Zimmermann Feb. 21, 2022, 7:54 p.m. UTC

Optimize performance of the fbdev console for the common case of
software-based clearing and image blitting.

The commit descripton of each patch contains resuls os a simple
microbenchmark. I also tested the full patchset's effect on the
console output by printing directory listings (i7-4790, FullHD,
simpledrm, kernel with debugging).

  > time find /usr/share/doc -type f

In the unoptimized case:

  real    0m6.173s
  user    0m0.044s
  sys     0m6.107s

With optimizations applied:

  real    0m4.754s
  user    0m0.044s
  sys     0m4.698s

In the optimized case, printing the directory listing is ~25% faster
than before.

In v2 of the patchset, after implementing Sam's suggestion to update
cfb_imageblit() as well, it turns out that the compiled code in
sys_imageblit() is still significantly slower than the CFB version. A
fix is probably a larger task and would include architecture-specific
changes. A new TODO item suggests to investigate the performance of the
various helpers and format-conversion functions in DRM and fbdev.

v2:
	* improve readability for sys_imageblit() (Gerd, Sam)
	* new TODO item for further optimization

Thomas Zimmermann (5):
  fbdev: Improve performance of sys_fillrect()
  fbdev: Improve performance of sys_imageblit()
  fbdev: Remove trailing whitespaces from cfbimgblt.c
  fbdev: Improve performance of cfb_imageblit()
  drm: Add TODO item for optimizing format helpers

 Documentation/gpu/todo.rst             |  22 +++++
 drivers/video/fbdev/core/cfbimgblt.c   | 107 ++++++++++++++++---------
 drivers/video/fbdev/core/sysfillrect.c |  16 +---
 drivers/video/fbdev/core/sysimgblt.c   |  49 ++++++++---
 4 files changed, 133 insertions(+), 61 deletions(-)