[CentOS] Intel Xeon and hyperthreading

[Les Mikesell]

On Thu, 2006-06-08 at 11:33 -0400, Sam Drinkard wrote:

> I suppose, without having extensive knowledge about how the model 
> behaves internally, or for that matter, writing to disk, it really would 
> be trial and error.  There are tools, but I'm not experienced enough to 
> know what they are really telling me either.  I know the model does a 
> lot of reads from data, but don't know if that data is cached on read, 
> or if the whole file is read in at once, then the numbers are crunched 
> and written or what.

vmstat and iostat will a reasonable idea of what is happening swap
and disk-wise if you watch them with a 1 or 5 second interval while
the app runs.  Note that disk writes are normally queued and especially
for scsi have little CPU overhead.  Reads often mean that the
CPU is waiting.  Depending on whether the same thing is read more
than once or not you might be able to speed this up with more
RAM to cache it.  But, if sar is reporting near 100% CPU use for
most of the run there probably isn't much you can do.

> I've posted some questions to the WRF-model.org website so maybe one of 
> the developers or someone with extensive software background info will 
> respond.  I know a lot of the weather oriented people who run the model 
> have little to no clue about unix or linux in general, just based on the 
> questions I see posted.

A different algorithm, or something like pre-sorting the data might make
a huge difference.

-- 
  Les Mikesell
   lesmikesell at gmail.com