[mythtv-users] Howto prevent MythTV flushing/Syncing disk writes (LiveTV/Recordings)

[Albert Graham]

David Brodbeck wrote:
> On Mar 18, 2008, at 11:24 AM, Albert Graham wrote:
>   
>> Also, that argument does not hold much water, because MythTV can  
>> handle
>> multiple feeds/cards at once, so if you have 5 cards (and I plan to  
>> have
>> at least 10) you'd be dead in the water.
>>     
>
> Well, yes, but again that data comes in small (but time-critical) chunks
>
>   
>> I imagine the frame buffer side of things is interrupt driven in most
>> cases, so if there are no conflicts in the hardware setup it should  
>> not
>> miss any frames, so write caching would actually improve this  
>> situation.
>>     
>
> I think the problem comes when the system is unable to service a video  
> interrupt in time because it's busy servicing a large disk write.
>   
Dave,

However, this can never be the case because the video capture interrupt 
will simply interrupt the disk write (which is actually for the most 
part in a I/O wait state doing nothing).

Most disks can write at 60MB/s - I mean, even the crappy ones, so why 
are we writing in 2-3MB/s  and syncing!, by that augment too, the 
syncing would cause loss of frames/interrupt - but that is not the case.

Like I said, my disks can write a 1G file - (fully flushed in under 2 
seconds - and the CPU is free during this time!), so the argument about 
the "some hardware" loosing frames is hardware that is limited by design 
(limited PIC etc..)  - i.e. not a PC, but some embedded set top box stuff.

Albert.