[gst-devel] mini filesrc patch

[Erik Walthinsen]

On Sun, 30 Sep 2001 vishnu at pobox.com wrote:

> i don't understand why touch is currently set to TRUE.
> -  src->touch = TRUE;
> +  src->touch = FALSE;

The touch param causes filesrc to read a word at the beginning of each
page.  This forces the kernel to read the data from the disk into
bufcache.  The reason this is necessary and on by default is that without
it, the first element to touch the data has to wait for the data to come
off disk.  In a bandwidth/latency critical situation, you'll have a thread
containing the filesrc and one or more threads containing the rest of the
pipeline.  The goal of this is to use the filesrc thread to manage the
disk I/O, which when using mmap means touching the data, which isolates
the latencies of doing so in their own thread, behind a queue that can
help absorb them.

      Erik Walthinsen <omega at temple-baptist.com> - System Administrator
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