July 7th, 2008


Why Computers Are Getting Slower (And What We Can Do About It)


Access latencies, in CPU cycles

(Note: old CPUs took multiple cycles to run one instruction
while new CPUs can run multiple instructions per cycle)

CPU        L1 cache   L2 cache   RAM         Disk
386                                2       500000
486               2               10      1800000
586               2               20      1500000
Pentium II        2         10    35      2400000
Pentium III       2         15    50      6000000
Pentium 4         3         25   200     18000000
Core 2            3         25   200     24000000



- CPUs are fast, communication between CPUs is slow
* Maximize performance by minimizing communication

- Fine-grained locking increases parallelism, but also increases inter-CPU communication!
* Worked great in the 1990's, but no more

- Writing to common data structures invalidates cache lines and increases inter-CPU communication
* Write mostly to thread-local data, read mostly from shared data

* Use NUMA/SMP friendly runtimes (JVM, etc)


And we wonder why cache-aware data structures are so much faster on modern hardware. How about that order of magnitude jump from L1 to L2 cache? And then again from L2 to RAM!

See also: RAM is the new disk (and disk is the new tape).
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Wanna cut those loose threads off your jeans? NOT IN ENGLAND!

Prime Minister Gordon Brown has argued that anyone over 16 caught with an illegal knife should be prosecuted, rather than escaping with a caution. But Mr Cameron says the presumption should go further - so anyone convicted of carrying a knife should be jailed.


I wonder who gets to decide what an "illegal knife" is? You suppose they put it up for popular vote?

Wind turbines generate too much power - overload grid!

The wind huffed, and it puffed, and it nearly caused major problems in the Northwest's electrical grid last week. A surge of wind last Monday afternoon jumped far beyond levels forecast by operators of Oregon's burgeoning wind-farm industry, sending more power into the regional grid than it could handle.


Suntory Mermaid II arrives home. US->Japan 110 days propelled purely by waves.

Japanese sailor and environmentalist Kenichi Horie has completed a 110-day solo voyage across the Pacific Ocean in a boat propelled by wave power to claim another world first. Weak waves and opposing ocean currents delayed his arrival, which was originally set for late May.

"When waves were weak, the boat slowed down. That's the problem to be solved," the adventurer told reporters Saturday from aboard his catamaran Suntory Mermaid II off the Kii Peninsula in western Japan. The 9.5 metre (31-foot) boat is equipped with two special fins at the front which can move like a dolphin's tail each time the vessel rises or falls with the rhythm of the waves.

"Throughout history, mankind has used wind for power, but no one has appeared to be serious about wave power," Horie told AFP last December. "I think I'm a lucky boy as this wave power system has remained virtually untouched."



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