[mythtv-users] Storing recordings on network share
linux at thehobsons.co.uk
Fri Sep 23 18:40:36 UTC 2011
Travis Tabbal wrote:
>>How is the size of that buffer determined ?
>It was hardcoded last time I looked in the source.
Correct, I've downloaded the source to have a look, and I see that it
is indeed configured there.
TFW_DEF_BUF_SIZE = 2*1024*1024;
TFW_MAX_WRITE_SIZE = TFW_DEF_BUF_SIZE / 4;
TFW_MIN_WRITE_SIZE = TFW_DEF_BUF_SIZE / 32;
Now, I've never programmed in C or C++, but with the comments I can
get a jist of some of what the code is doing.
So our buffer is by default only 2MByte. That's as short as only a
couple of seconds, even at our DVB-T SD rates. That seems incredibly
small to me.
Can someone confirm that even while we are syncing the file (one
thread), we are still able to send file data to the kernel (separate
thread) - ie writes from buffer to kernel aren't blocked by the
earlier writes being synced to disk ? If that is the case, then I can
see how this arrangement works - as long as the kernel itself will
accept more data into it's buffers, then we'll have no problem
keeping this buffer reasonably available. But, if we block writing to
the kernel, then this buffer will fill up and we'll lose data.
One last thing. Is it easy to build just this one bit of code
(library ?) ? I'd kinda like to try a larger buffer size and see if
it makes any difference - but I don't want to rebuild everything
(I've only built the whole thing as per the install instructions) and
risk breaking my setup.
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