----- Original Message ----- > From: "John A. Sullivan III" <jsulli...@opensourcedevel.com> > To: spice-devel@lists.freedesktop.org > Sent: Friday, June 17, 2011 5:25:16 AM > Subject: [Spice-devel] Meaning of compression settings in qemu > Hello, all. I did take Marian's advice and peruse the qemu man page > but, after lots and lots of Internet searching and document reading, > I'm > not quite clear on exactly what the compression settings mean in qemu. > This is important to us as we need to optimize for an entirely WAN > based > environment. > > I see we have: > image-compression=[auto_glz|auto_lz|quic|glz|lz|off] > I understand that glz uses a dictionary to reduce bandwidth > consumption > and is used for artificial images and quic is used for more > photo-realistic images. I gather this is handled by SPICE > automatically. Does that mean the difference between auto_glz and > auto_lz is whether it chooses glz or lz (non-dictionary based) for the > artifical bitmap compression? Does choosing quic, glz, or lz mean that > is the only algorithm used and automatic selection based upon the type > of image is disabled?
I do believe you got it right, please anyone, correct me If I am wrong. > > Then we have: > jpeg-wan-compression=[auto|never|always] > zlib-glz-wan-compression=[auto|never|always] > > I have noticed while watching stdout/stderr on the host that there > does > seem to be some way that the host senses the bandwidth of the client. > So is jpeg-wan-compression to determine IF it compresses (and if so, > what is the difference between that and the above image-compression > parameter?) and zlib-glz-wan-compression to determine HOW it > compresses > if it is supposed to, i.e., with lossless GLZ alone or with lossy zlib > on top of GLZ? > > What is the overhead associated with simply leaving these on auto? ALL > of our users are outside of the data center but the whole point of the > organization is to be mobile. Thus, one day, the user may be accessing > their Virtual Desktop on a PC at the end of a 100 Mbps WAN link and > the > next from their netbook tethered through their cellular phone. Thus, > it > would be great to dynamically adapt but, given the overhead of > adapting > and the low likelihood of someone being on a 100 Mbps WAN link, should > we just set them all to always compress as if on a low bandwidth link? As I believe the concept is: Once client connects to a guest, "spice server" determines client's bandwidth (look at code for details, I believe It could be more appropriate and guys are working on it). "jpeg-wan-compression" and "zlib-glz-wan-compression" are enabled in case the client's bandwidth is <10Mbps, otherwise It's disabled. When jpeg compression and zlib over glz compression are enabled then photo-like bitmaps are compressed by lossy jpeg compression and textual/artificial bitmaps are compressed by lossy zlib on top of GLZ. That's what I described is default behaviour (jpeg-wan-compression=auto, zlib-glz-wan-compression=auto). Options always/never cause that jpeg/zlib over glz compressions are always/never enabled regardless of calculated bandwidth. > > Thanks - John > > _______________________________________________ > Spice-devel mailing list > Spice-devel@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/spice-devel _______________________________________________ Spice-devel mailing list Spice-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/spice-devel
