[Spice-devel] xf86-video-qxl performance

[Jeremy White]

> Actually, for WAN, we require ACK for 40 messages, but we allow sending
> up to 80, without getting an ack for the first 40.
> From my experience with Windows guest, it sounds like the DRAW_FILL
> commands might be related to anti aliasing, and maybe the future RENDER
> support that Alon mentioned will indeed help with this. Meanwhile I
> would also try to disable off-screen surfaces, as was also mentioned in
> a previous reply,

Ah, yes, sorry; I knew 20 was imprecise.   But (500 / 80) * 80 ms is
still a good bit of delay.

Increasing the ack window (and pipe size) by a factor of 10 makes the
first apparent problem vanish.

Disabling off screen surfaces has the same user visible effect.

Note, though, that I have the luxury of focusing on a long term agenda,
so I'd rather pursue the 'best' solution (at least for now).


> What OS your client has? When spice-server identifies WAN, it
> automatically turn on Nagle's for the display channel (turns off
> TCP_NODELAY), which should aggregate small tcp messages. However, it has
> bad interaction with the delayed acks on the client side (especially in
> Windows clients, where the default delayed ack timeout is 200ms iirc),
> and overall it can lead to bigger latency between operations. We are
> planning to get read of this, and aggregate the messages on the
> application layer instead.

I'm currently testing with Debian testing, although our eventual
deployment platform will be a heavily modified RHEL 6 system.  The
pointer to TCP_NODELAY is also a good one; I'll play with that and see
what effect it has.

> Just to clarify, we currently don't condense messages in spice-server,
> though it is another item in our TODO.

Ah, okay, that's helpful (although there is some very limited pruning in
red_worker.c, no?)

Is that todo on anyone’s immediate radar?  I'm certainly not qualified,
but it seems like that could have an major impact on what we're trying
to achieve (regular Office applications hosted on a pure Linux server
across a WAN).  So perhaps I need to become qualified :-/.

Cheers,

Jeremy