[Spice-devel] [PATCH spice 1/3] dcc_compress_image: Handle NULL drawable

[Frediano Ziglio]

> 
> On Thu, 2016-01-14 at 12:07 -0500, Frediano Ziglio wrote:
> > > 
> > > On Thu, Jan 14, 2016 at 10:27:02AM -0500, Frediano Ziglio wrote:
> > > > Had a small discussion with Pavel.
> > > > We agree that original code is quite complicated and is hard to
> > > > understand
> > > > the final compression format used.
> > > > 
> > > > So we would like to have some public discussion about the topic.
> > > > 
> > > > I personally agree we should have a single code deciding the
> > > > compression
> > > > to use.
> > > 
> > > I definitely agree here. For one, having different compression being
> > > used depending on whether the qxl driver is used or not is unexpected
> > > (eg if you set image compression to glz, lz will still be used during
> > > initial bootup, and then will 'switch' to glz later on. I haven't looked
> > > at the code, so there might be good reasons for that).
> > > 
> > > > 
> > > > This is the list of actual compressions:
> > > > - AUTO_GLZ;
> > > > - AUTO_LZ;
> > > > - QUIC;
> > > > - GLZ;
> > > > - LZ;
> > > > - LZ4.
> > > > A client can also decide to disable compression.
> > > > 
> > > > The AUTO_XXX looks like they should use QUIC as a fallback if XXX is
> > > > not
> > > > possible or if an image with high graduality is detected.
> > > 
> > > (side question, do we have numbers on compression ratio and cpu usage
> > > for quic/lz/glz/lz4?)
> > > 
> > 
> > Brief and raw of a Windows replay capture
> > 
> >         Images  MB before   MB after  Ratio     CPU time
> > LZ4     193     24.21       2.43      10.04%    0.04
> > QUIC    204     23.11       1.66       7.18%    0.44
> > GLZ     190     20.05       1.2        5.99%    0.14
> > LZ      202     20.42       2.04       9.99%    0.15
> > 
> > So why use Quic ?
> 
> Interesting data. Indeed, QUIC seems to be the worst choice. from this data,
> it
> seems that you'd want GLZ if you were optimizing for network bandwidth, and
> LZ4
> if you're optimizing for CPU usage. Might be nice to see data for a slightly
> larger sample as well.
> 
> Out of curiosity, did you write a little utility for doing this benchmark, or
> did you just modify the code in-place?? Having a little benchmark utility
> that
> you could run on different replay captures might be a useful thing to have in
> the repository...
> 
> Jonathon
> 
> 

No code modification at all. Compile with COMPRESS_STAT enabled, run replay
utility with SPICE_DEBUG_LEVEL=3 set at the end you see a similar table
(I added just ratio with LibreOffice calc).
Oh... you just need to use -C replay option with
- 4 quic
- 5 glz
- 6 lz
- 7 lz4
(not sure about 5/6, maybe swapped).
I think would be really helpful to collect different replay captures of
normal day job.

Frediano