[PATCH v2 0/8] Add new formats support to vkms

[Pekka Paalanen]

On Wed, 10 Nov 2021 14:32:26 -0300
Igor Torrente <igormtorrente at gmail.com> wrote:

> Hi Pekka,
> 
> On Tue, Nov 9, 2021 at 6:32 AM Pekka Paalanen <ppaalanen at gmail.com> wrote:
> >
> > On Tue, 26 Oct 2021 08:34:00 -0300
> > Igor Torrente <igormtorrente at gmail.com> wrote:
> >  
> > > Summary
> > > =======
> > > This series of patches refactor some vkms components in order to introduce
> > > new formats to the planes and writeback connector.
> > >
> > > Now in the blend function, the plane's pixels are converted to ARGB16161616
> > > and then blended together.
> > >
> > > The CRC is calculated based on the ARGB1616161616 buffer. And if required,
> > > this buffer is copied/converted to the writeback buffer format.
> > >
> > > And to handle the pixel conversion, new functions were added to convert
> > > from a specific format to ARGB16161616 (the reciprocal is also true).
> > >
> > > Tests
> > > =====
> > > This patch series was tested using the following igt tests:
> > > -t ".*kms_plane.*"
> > > -t ".*kms_writeback.*"
> > > -t ".*kms_cursor_crc*"
> > > -t ".*kms_flip.*"
> > >
> > > New tests passing
> > > -------------------
> > > - pipe-A-cursor-size-change
> > > - pipe-A-cursor-alpha-transparent
> > >
> > > Performance
> > > -----------
> > > Following some optimization proposed by Pekka Paalanen, now the code
> > > runs way faster than V1 and slightly faster than the current implementation.
> > >
> > > |                          Frametime                          |
> > > |:---------------:|:---------:|:--------------:|:------------:|
> > > |  implmentation  |  Current  |  Per-pixel(V1) | Per-line(V2) |
> > > | frametime range |  8~22 ms  |    32~56 ms    |    6~19 ms   |
> > > |     Average     |  10.0 ms  |     35.8 ms    |    8.6 ms    |  
> >
> > Wow, that's much better than I expected.
> >
> > What is your benchmark? That is, what program do you use and what
> > operations does it trigger to produce these measurements? What are the
> > sizes of all the planes/buffers involved? What kind of CPU was this ran
> > on?  
> 
> 1 and 2) I just measured the frametime of the IGT test ".*kms_cursor_crc*"
> using jiffies. I Collected all the frametimes, put all of them into a
> spreadsheet, calculated some values and drew some histograms.
> 
> I mean, it is not the best benchmark, but at least give an idea of what
> is happening.
> 
> 3) The primary plane was 1024x768, but the cursor plane
> varies between the tests. All XRGB_8888, if I'm not mistaken.
> 
> 4) I tested it on a Qemu VM running on the Intel core i5 4440. ~3.3GHz

Hi Igor,

alright, that analysis sounds fine, even though varying cursor plane
size is casting some ambiguity on the results.

If you want to dig deeper into measuring this, I would suggest some
scenarios if at all possible:

- large primary plane and large cursor plane with 100% overlap, to
  measure the raw pixel throughput

- large primary plane and small cursor plane with 100% overlap, to
  measure the efficiency of skipping pixels that do not need blending

- large primary plane and large cursor plane with only a little
  overlap (cursor largely off-screen), to measure the efficiency of
  skipping pixels that do not contribute to the end result at all

But that's only curiosity, I think your existing benchmarks sound
perfectly fine as the difference is so big.


Thanks,
pq
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