

Effect of memory bandwidth on GPU performance - suraj
http://www.realworldtech.com/page.cfm?ArticleID=RWT042611035931

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JoeAltmaier
Pipeline depth is also important for the end experience - which shows up as
milliseconds of lag. ARM by SG kept getting faster by expanding the pipeline
(30+ levels?) but only when the pipeline wasn't blown. Is that happening with
high-end GPUs?

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thesz
<http://lambda-the-ultimate.org/node/1277>

Tim Sweeney said from experience that every single precision flop/s need
byte/s of bandwidth.

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nightlifelover
No comment about that?! We need faster DRAM!!

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wtallis
No, we don't. GDDR5 is faster than current cards can handle. The bottleneck is
in the memory controllers themselves - beyond an effective data rate of 5Ghz,
the memory controllers get really complicated and just plain large.

A Radeon 6970 ships with GDDR5 that can run at 6Ghz effective rate, but it
only runs it at 5.5Ghz (though there are factory-overclocked cards that reach
at least 5.7Ghz). NVidia's cards tend to run their memory at no more than
4.5Ghz effective, though they compensate by using a wider memory bus (which
accounts for the odd-looking memory sizes).

Upper-mid-range cards built off smaller cores tend to have higher core clocks,
but much lower memory speeds. Halving the number of compute units decreases
the demand for memory bandwidth enough that it's not crippling when you use a
memory controller that's half the size and can only run at 75% the speed,
which saves the manufacturer a lot of money.

