[vdr] Re: max. latency time to large, bad response from vdr

[Emil Naepflein <Emil.Naepflein@philosys.de>]

On Wed, 23 Jul 2003 16:47:13 +0200, Carsten Koch <Carsten.Koch@icem.de>
wrote:

> > The next step for me would be
> > to keep the read info until there is any change by adding or deleting
> > any recordings and change of modification time of the primary video
> > directory. 
> 
> You have to be careful here.
> The modification time does not propagate up the directory tree:
<snip>
> So I guess it is not sufficient to monitor the modification time of
> the primary video directory.

This was just an idea to cover simple manual changes. It is clear that
if you make manual changes in the tree then there is a problem. We just
have to avoid doing stats on all directories in the tree because excatly
this takes so long. If changes are done only by vdr it is easy to
invalidate the cache. For external manual changes it should be easy to
do a touch to the video directory only after the changes to give vdr a
chance to update the cache. Expiring the cache is no solution because
then it has to be reread to often which takes time. A more complicated
solution would be to do the reread in a separate thread in the
background.

> > It is really bad that Linux behaves that strange when reading/writing
> > large amounts of data. It should keep the file metadata incore instead
> > of pushing it out.
> 
> Yes.
> That is utterly brain-dead.
> The meta data is so small, it could be kept in memory most of the time
> without significant loss of buffer space.
> In many situations, the buffered data will never be used again and all
> they do is push more important data out.
> Maybe we should post a suggestion onto the XFS mailing list?

I have proposed this already to Reiser but I have not much hope that
there will be any change soon. BTW, I have dropped XFS because it is
very slow on file creation and file deletion compared to reiserfs and
even ext3 (bonnie test). I now use ext3 as best compromise and I am
happy so far.

Emil


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