[GRASS-SVN] r48393 - grass-addons/vector/v.surf.icw

[svn_grass at osgeo.org]

Author: hamish
Date: 2011-09-21 02:55:36 -0700 (Wed, 21 Sep 2011)
New Revision: 48393

Modified:
   grass-addons/vector/v.surf.icw/description.html
Log:
linux I/O performance tuning hints

Modified: grass-addons/vector/v.surf.icw/description.html
===================================================================
--- grass-addons/vector/v.surf.icw/description.html	2011-09-21 07:28:22 UTC (rev 48392)
+++ grass-addons/vector/v.surf.icw/description.html	2011-09-21 09:55:36 UTC (rev 48393)
@@ -34,6 +34,21 @@
 complete. A common use for that might be to only present data within
 a certain distance (thus confidence) of an actual sampling station.
 In that case the <em>r.cost</em> module can be used to create the mask.
+<P>
+This module writes lots of temporary files and so can be rather disk I/O
+intensive. If you are running it many times in a big loop you may want to
+set up a RAM-disk to put the mapset in (on UNIX symlinking back into the
+location is ok), or adjust the disk-cache flushing timer to be slightly
+longer than one iteration of the script.
+<BR>To do this on Linux you can tune the
+ <tt>/proc/sys/vm/dirty_expire_centisecs</tt> kernel control. The default
+is to keep files in memory a maximum of 30 seconds before writing them to
+disk, although if you are short on free RAM the kernel may write to disk
+long before that timeout is reached.
+<!-- Linux I/O tuning hints:
+   http://www.westnet.com/~gsmith/content/linux-pdflush.htm
+   http://tldp.org/LDP/sag/html/buffer-cache.html
+ -->
 
 
 <H2>EXAMPLE</H2>