Re: [Qemu-devel] [PATCH] vnc: allow fall back to RAW encoding

[Peter Lieven]

Am 28.08.2015 um 13:56 schrieb Gerd Hoffmann:
> On Do, 2015-08-27 at 14:46 +0200, Peter Lieven wrote:
> > I have observed that depending on the contents and the encoding it happens
> > that sending data as RAW sometimes would take less space than the encoded data.
> > This is especially the case for small updates or areas with high color images.
> > If sending RAW encoded data is beneficial allow a fall back to RAW encoding
> > for the framebuffer update.
> Do you happen to have some stats for this, especially the "small update"
> case?  We might want to go straight to raw (without trying other
> encodings) for small updates, to avoid encoding things twice.

I had a look at hextile, zrle, tight and zlib encoding. It seems that the case
that raw encoding is smaller never happens for zrle and tight. For zlib and
hextile its quite common, but there is no obvious mark for the size of the
update. It seems to heavily depend on the contents as assumed earlier.

I understand your concern of twice encoding, but I think there is no easy
way to avoid this. However, sending the data as raw later on is a cheap
operation because the patch only does it when no pixel conversion has to be 
made.

Peter