[mythtv-users] Latency timings...

Steven Adeff adeffs.mythtv at gmail.com
Fri Apr 14 23:22:36 UTC 2006


On 4/14/06, Brian Wood <beww at beww.org> wrote:
> On Apr 14, 2006, at 2:47 PM, Steven Adeff wrote:
> > Couple questions....
> >
> > 1)
> > Is there a reason setpci wouldn't work? I run:
> > setpci -v -s 00:0a.0 latency_timer=80
> > or
> > setpci -v -s 00:09.0 latency_timer=80
> > for my two SATA devices  and it shows:
> > 00:09.0:0d 80
> > but when I check with lspci -v they're both still set to zero?
>
> Some chipsets seem to report a latency of zero no matter what you do.
> In those cases you can adjust the values for things capture cards and
> video cards but can't adjust the disk systems. Playing with latency
> values is something that sometimes helps some people but is not a
> panacea.
>
>
> >
> > 2)
> > The wiki page doesn't give much help in the advice area as to latency
> > values or how to "calculate" them for Myth use (ie DVB cards, etc),
> > except to say that your harddrives should have a higher value than
> > your PVR card. Anyone have any advice in this area?
> >
>
> It's pretty much a trial and error thing at this point. The mobo
> manufacturers don't seem to give out much info, they just assume that
> you will be running Windows and be happy.
>
> The "optimum" values are so subject to so many variables that any
> attempt to give advice is doomed failure, you just want to understand
> the general principles well enough to make somewhat intelligent
> adjustments, but the exact correct value will depend on what type and
> how many video streams are being delivered, what sort of storage
> system they are being delivered to, the buffer capacity of everything
> involved in the system, what other devices are competing for time on
> the PCI bus, what interrupts might be shared and many more that I
> have not even thought of I'm sure.
>
> The purpose of the WiKi entry was basically to let people know what
> the parameter is, the fact that it can affect performance of a Myth
> system and what that error you sometimes get from the IVTV drivers in
> your boot log might mean.

gotcha. thanks for clearing this up. I'll let it be and be happy
everything works fine =)
(damnit steve, stop trying to optimize!)

--
Steve


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