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

Albert Graham agraham at g-b.net
Tue Mar 18 22:21:23 UTC 2008


David Rees wrote:
> On Tue, Mar 18, 2008 at 6:09 AM, Albert Graham <agraham at g-b.net> wrote:
>   
>> Does anyone know how to prevent MythTV from flushing/syncing every
>> single write request when watching LiveTV or  recording something.
>>
>> My machine has lots of memory and very large fast disks, so I would
>> prefer writes to occur in much larger chunks and a lot less often,
>> rather than every 3 or so MB.
>>     
>
> Yes, as David Brodbeck mentioned, MythTV explicitly syncs video data to
> disk every 250ms or so because "back in the day" some systems did
> encounter hiccups when letting the OS flush data out to disk as it saw
> fit. In some cases the amount of time it took to flush data to disk
> took to long so this would cause playback to hiccup as the disk was
> too busy writing (and not enough video was buffered to make up for it)
> or recordings to hiccup as the disk writing process interrupted the
> read process.
>
>   
Ah, It's understandable that "playback" could get interrupted - because 
as far as I remember,
by default writes get priority over reads (this a configurable /proc 
option in Linux), I interpreted
 "video skipping" as failed capturing - which is different from frontend 
playback, my apologies :).

> I also would prefer to let the data get flushed out automatically as
> this would reduce the constant clatter of the disks. Or at least make
> the sync interval configurable.
>   
me too.
> If you want to fix this, you're going to have to dig into the source code.
>   
I'm not a C programmer (spent 20 years programming in assembler) so I 
may just learn C sometime soon and start
 to contribute to MythTV.
> -Dave
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