Subject: Re: Got CUDA
From: Skywise
Date: 16/04/2009, 06:14
Newsgroups: alt.sci.seti

DaveT <svirtftcyt@yahoo.com> wrote in
news:aircu4t2pc02k1salenm7qq2tjes76epsj@4ax.com: 

BTW, my machine is chewing through these CUDA units in about
2:15 - 2:30.

CUDA workunits do not report time properly. The 'time' shown
is CPU time, not wall-clock time. The CPU time shown is just
the small amount of CPU that has been used to keep feeding
data to the GPU.

CUDA does not run 100% on the GPU. A tiny piece also runs
on one of the CPU cores, which I understand is the overhead
to monitor the GPU and send it data.

You can test this by waiting for a CUDA work unit to start
and noting the time on a clock, then noting the same clock
when the work unit is done.

A side effect of this is - at least with my versions, it
may have been fixed? - is that when BOINC requests more
work units for CUDA, it keeps asking for more and more and
more. It thinks a work unit only takes 3 minutes (CPU time),
and if you're set to download 1 days worth, it tries to
download 480 work units (broad generalization).

So you'll have to watch that you don't download too many work
units. I have to watch this because I like to keep several
days of work on the drive for those inevitable server outages.

Brian
-- http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html Quake "predictions": http://www.skywise711.com/quakes/EQDB/index.html Sed quis custodiet ipsos Custodes?