[mythtv] waiting for prebuffer...

[John Patrick Poet]

In general you should not mix top/bottom posting.  Isaac prefers that 
everyone standardize on bottom posting (which I am violating, since you 
did ;-) ).

Anyway, MTU stands for "Maximum Transmission Unit".  Basically it is the 
maximum size of packet of information sent over ethernet at one time.

By lowering the MTU on my system, I am forcing it to send the data in 
smaller pieces.  This can actually increase the "quality of service", 
since large packets from "other" apps can hog the pipe.  The frontend 
does not need a lot of data at one time, but it needs it to arrive 
frequently/consistently.

On my system, I changed the MTU using this command:

ifconfig eth0 mtu 800 up

This does NOT survive a reboot, and may not work for your flavor of 
linux or your NIC, although it should.

On my system, I added a line which says "MTU=800" to 
"/etc/sysconfig/network-scripts/ifcfg-eth0".  This causes the MTU to be 
set to 800 when the eth0 interface is initialized during bootup.

John


Robert Rozman wrote:

>Hi,
>
>sorry for dummy question: what is MTU and how to set its value ?
>
>Regards,
>
>Robert.
>
>----- Original Message ----- 
>From: "John Patrick Poet" <john at BlueSkyTours.com>
>To: "Development of mythtv" <mythtv-dev at mythtv.org>
>Sent: Monday, September 27, 2004 10:35 PM
>Subject: Re: [mythtv] waiting for prebuffer...
>
>
>
>On Mon, 27 Sep 2004, Thomas Börkel wrote:
>
>  
>
>>HI!
>>
>>John Patrick Poet wrote:
>>
>>    
>>
>>>>Does it help at all if you uncomment the calls to run the decoder at
>>>>realtime priority?  (This is not a good idea in general -- sometimes
>>>>makes the videoout thread starved for cycles and jittery -- but if it
>>>>improves matters might indicate that the decoder thread's starved for
>>>>CPU).  Could the driver for your gigabit ethernet be hogging CPU for
>>>>longish periods?  Can you try to make the MTU smaller?
>>>>        
>>>>
>>>The typical load on the frontend is just a touch over 1, with between 40
>>>and 45% CPU.
>>>
>>>I have had this problem since before you added the "realtime priority",
>>>so I don't think that has anything to do with it.
>>>
>>>I need to some more testing, but it actually looks like lowering the MTU
>>>has solved the problem!  The problem is infrequent enough that I cannot
>>>be sure, but I have not seen a glitch in over an hour, now.
>>>      
>>>
>>To what value did you set the MTU? And did you lower it only on the
>>frontend?
>>
>>Thomas
>>
>>    
>>
>
>Actually, I only lowered on on the backend.  I just randomly choose 800, and
>it does seem to have fixed the problem.
>
>I use my backend for other things, several of them internet related, so I
>assume that even though it has a gigabit NIC, that service times were too
>long.
>
>John
>
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