[gst-devel] On the plugin cache

[Simon Holm Thøgersen]

[ Resending as this one didn't seem to reach the list. ]

ons, 05 11 2008 kl. 21:51 -0500, skrev Behdad Esfahbod: 
> So how should the cache work?  By comparing the timestamp of each plugin dir
> to the recorded timestamp of that dir in the cache.  One must compare
> timestamps for equality, not for being more recent as that is prune to clock
> skew false negatives.

I completely agree with you Behdad that excessive work is being done
when stating files and not just dirs. However, even with the current
design it is not where most of the time is spent.

The following is a profile of my laptop (Intel Pentium-m @1.5GHz)
running 'gst-launch-0.10 --gst-disable-registry-fork' with 157 plugins
present:

total 22 ms
  linking libs 4.1ms
  gst_init 17.9 ms
    misc 3.3 ms
    loading registry.i686.bin 12.4 ms
      crc 1.5 ms
      creating elements 10.9 ms
    stating 2.2 ms

I have a very simple patch that almost halves the time spent stating
that I did almost a year ago but never got around to posting; I'll do
that now.

Back then I also looked at speeding up the creation of elements.
According to a comment I made back then it should be possible to reduce
the time with 75%. I'm pretty sure that some of the changes broke ABI,
but I'm not sure whether those that did were responsible for the
speedup. I might try to port the work I did back then to the current
gstreamer.

Before I look more into this, it would be nice if others posted similar
profiles for their systems that could confirm this distribution. To
generate my profile I added a bit of custom debug for the crc part, but
the following should be sufficient for the rest.

export GST_DEBUG=3
time /usr/bin/gst-launch-0.10 --gst-disable-registry-fork

The value of doing the crc check seems pretty dubious to me btw; if
you've got disk corruptions there are plenty of other ways your system
could malfunction. It should be pretty easy to make it optional at load
time though.


Simon Holm Thøgersen