[Beowulf] Moores Law is dying
larry.stewart at sicortex.com
Wed Apr 15 06:27:20 EDT 2009
Steve Herborn wrote:
> There are disciplines like EDA which generate large programs today.
> Computer generated, of course. Companies like Intel and AMD use these
> programs to design microprocessors. So yes, their architects are well aware
> of this issue.
In particular, compiled simulators, which use very long straight line
code to evaluate what the gates are doing in the correct order, every
cycle. The simple ones evaluate every gate every cycle, the complicated
ones figure out what blocks of gates can be skipped. These things
really stress i-stream bandwidth.
I've not heard of multicore or cluster versions of these, but I'm not
paying much attention to it. Most design groups have so many test cases
to run that many copies of the simulator is just as useful as one faster
Compiled sims generate very large text segments. At one instruction per
gate, plus some overhead (loads and stores are "overhead" !) it is
pretty easy to get to gigabyte text. The counterpressure is the
performance - with 4 GB/s istream bandwidth it takes one second per
simulated cycle to run.
The point is that this class of large program does not have unmanageable
OT - I once was writing programs to generate programs with very large
basic blocks, maybe 50K instructions. It is a Big Mistake to try gcc
-O3 on these, the optimizer goes into brain freeze for 15 minutes or so...
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