[linux-dvb] Re: [PATCH] Skystar2 pid filters reorganization

[Holger Waechtler <holger@convergence.de>]

Ralph Metzler wrote:
> Roberto Ragusa writes:
>  > Every accepted packet is tested twice.
>  > Discarded packets are tested once (and very early).
>  > So we gain here and loose there.
>  > 
>  > In relation to "one of the first checks", do you think that the swfilter
>  > code is fast enough to let us just open_whole_bandwith when we're out of
>  > hw filters?
>  > 
>  > Consider that the unwanted/wanted ratio can be 5 or 10 in typical
>  > usage and much higher in particular cases (we have to open
>  > everything when scan is asking 10 pids).
>  > 
>  > What do you think?
>
> There is no reason it should not work. After all, it works fine with 
> the other budget cards without any hardware filters.
>
> The current linuxtv version filter even has a bigger lookup time
> (O(1)) to discard/accept filters compared to the older version with
> constant lookup time. But the latter only supported one filter per PID.
> One could write a new one with constant lookup and multiple filters if you
> really need it. But compared to e.g. the performance needed for MPEG2 
> decoding the difference is probably negligible.
In most scenarios you have only a few active filters, usually on less 
than 10 or 20 PIDs. If one really encounters performance bottlenecks in 
this code he is welcome to replace the linked list by a tree-alike 
structure or a PID table in conjuction with attached filter lists...

Holger



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