satyamdubey writes:
> I want to know how much does the interface width offset the extra
> number of CUDA cores in any gpu family. ...
Memory bandwidth is critical for good CUDA performance, though it does
vary a bit by application. I refer to it as, 'aggregate memory bandwidth
per CUDA core'. A GTX 780 has lots of cores, but it doesn't remotely have
the bandwidth to feed them, making it less efficient in how CUDA loads
can be parallelised. Thus, one 580 can beat a 780, and two 580s easily
beats a single Titan despite having less than half as many cores total. See:
http://www.tomshardware.com/reviews/geforce-gtx-760-review-gk104,3542.html
Toms doesn't have an AE CUDA test yet, but I'm hoping to help them out
with that in the Fall. In the meantime, see:
http://forums.creativecow.net/thread/2/1019120
> ... could they have used 512 CUDA cores and a 192 bit interface width
> to achieve similar results?
No; when the 580 was new, it was the top-end card, and NVIDIA knew that
providing 512 cores with a lot of bandwidth makes a big difference in
many situations, including gaming (heavy AA, high-res displays). What
NVIDIA has not done is make any kind of equivalent card today. The mem bw
of all the 700 series cards, and the Titan, really needs to be at least
2X more to feed that vast number of cores present (512bit minimum,
preferably more). In this respect, for CUDA, the 780 and Titan are
particularly disappointing. For the same cost as a single 780, one can
get four 580 1.5GB cards, or three 580 3GB cards, which would be much
better for AE. Other apps may vary, but tom's results show the 580 doing
very well in all CUDA tests except Fluidmark because that's an aggregate
result which includes normal 3D tests aswell.
So, for example, if you're building an AE system, it boils down to
budget. If you can afford it, get multiple Titans and benefit from the
larger RAM. If not, get used 3GB 580s.
For example btw, the last 580 1.5GB card I won on eBay only cost me 96.50 UKP
(about $150 US). My AE system has four 580 1.5GB cards, the total cost of
which was just 472 UKP - that's a quite a bit less than one 780 card, but
massively faster for CUDA.
Btw, the GTX 460 only has 336 cores, but already showed that having a
narrower bus can hurt performance in some situations (the standard 460
has a 256bit bus, the V2 card has a 192bit bus), so the difference is
clear even with much less cores than a 580. However, irony of the 460
is that the V2 card has higher clocks, creates much less heat and thus
can be oc'd way more than a normal 460 - one of my 460 V2s runs at
1025MHz with a lower vcore than my original 850MHz EVGA FTWs.
Ian.