[linux-dvb] Re: Quality of dvb-kernel in upcoming 2.6

[Michael Hunold <hunold@convergence.de>]

Hello Emard,

> To get a glance of new software, I upgraded my debian
> woody into upcomaing sarge (currently also named 'testing')
> and compiled latest kenel 2.6.0-test7 and applied patches
> (actually one patch from dvb-kernel 01-xx-something.
> another patch 03-xx-something failed).
These patches replace the static firmware blob with the generic 
"firmware_class" loading mechanism. They haven't been updated lately, 
because there are still problems with it. You shouldn't apply these 
patches (or at least read README.firmware... ;-)

Please try again with a fresh 2.6.0-test8 -- there, all the latest 
patches have gone in. 2.6.0-test7 is fairly old.

> if the frontend module is removed while the
> frontend is being used, the fronted process gets just
> a segfault and this removal no longer crashes the machine.
> Kudos to frontend people
Yes, this should be improved, ie. proper module locking for both 
frontend devices and drivers. Jon Burgess did a first try, but 
unfortunately the missed something, so the usage counter was screwed 
after a few device uses.

> Budget and network.
>
> I tested budget on my budget-patch card, but I think it should
> manifest on other budgets as well. So:
>
> On budget, mplayer can be used to watch some video transmission 
> but it seriously looses packets and skips frames.
Hm, I just tried with 2.6.0-test8 and had no problems recording 
something. No skips, but I admit that I have a perfect signal here, so 
users with weak signals might have problems that I haven't seen yet.

> On network at dvb-s, some packets seem to creep in now and then,
> it could be good for ping-ing somehost and doing few telnets
> but definitely far from the whole bandwidth. 
> (OK, on 2.4 is mostly the same thing and we know why)
The crc-checking code is currently broken in 2.6, but I don't know if 
network stuff uses crc-checking by default.

You might want to try to "makelinks" the dvb-kernel driver, because 
there have been fixes that I haven't sent to Linus yet.

> Moreover, if the dvb-ttpci is removed while network interface is
> active, the interface is not removed together with the driver and
> kernel will crash soon after. (On 2.4 network interfaces used to
> gracefully go away when the driver is removed)
Probably something within in the network device subsystem, which has 
changed in 2.6. recently. Probably this is a bug in the driver which did 
not look bad in 2.4...

> The mysterious packet loss can be seen with e.g. ethereal when the
> whole bandwidth is captured and then attempted to follow. (click on
> some tcp entry and select "Time-sequence graph (Stevens)"
> On X axis is time, on Y axis is byte offset. Discontinuities on
> Y axis. Packet loss denote vertical jumps or missing vertical dots 
> on the graph. Here I enclose 2 png's of ethereal, one having
> no packet loss and the other I draw red arrows at some packet loss 
> points, you could spot more...
Unfortunately, I don't have the time to work on the network stuff, so 
feel free to investigate this further and send a patch. 8-)

> Emard
CU
Michael.



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