[mythtv] Ticket #10414: HDHomeRun: Bad Recordings (was: Bad Recordings - Choppy Playback)

[Daniel Kristjansson]

On Sat, 2012-03-10 at 18:44 -0600, Marc Randolph wrote:
> On Sat, Mar 10, 2012 at 10:41 AM, Daniel Kristjansson
> > Can you take a look at this:
> >  http://www.cyberciti.biz/faq/linux-tcp-tuning/
> > And tell me if increasing the rmem_max helps?
> > libmythhdhomerun tries to increase the socket buffer
> > on startup, but perhaps the rmem_max is set low on
> > your system? Mine is set to 131071000.
> 
> Wow.  http://fasterdata.es.net/fasterdata/host-tuning/linux/ seems to
> suggest that values 10x smaller would be about good enough for a 10
> Gbps network, and that going overboard actually hurts performance.
> Wonder which site is right.

Mine is undoubtedly much higher than it needs to be. But setting the
_max values higher never has a negative impact on performance. All it
does is allow applications to set the value that high. MythTV won't
set it that high and most applications will use the default.

wmem_default is only one that can get you in trouble as a networking
end point. If you set the buffering too high it can break the
assumptions in TCP and other dynamically scaling protocols. With
udp and rtp streaming this isn't an issue though. Either you have
sufficient bandwidth or not, packets are never resent and the
HDHomeRun can't send the data at a lower rate because of the
limited bandwidth.

BTW Anyone using a recent HDHomeRun firmware is using rtp streaming.

-- Daniel