Multithreading - What's it Mean to Developers?

sysadmn writes "Yet another reason not to count Sun out: Chip Multithreading. CMT, as Sun calls it, is the use of hardware to assist in the execution of multiple simultaneous tasks - even on a single processor. This excellent tutorial on Sun's Developer site explains the technology, and why throughput has become more important than absolute speed in the enterprise. From the intro: Chip multi-threading (CMT) brings to hardware the concept of multi-threading, similar to software multi-threading. ... A CMT-enabled processor, similar to software multi-threading, executes many software threads simultaneously within a processor on cores. So in a system with CMT processors, software threads can be executed simultaneously within one processor or across many processors. Executing software threads simultaneously within a single processor increases a processor's efficiency as wait latencies are minimized. "

Comments

stackless..

[joeldg]

this makes me wonder what the effect would be on something like stackless python?
the whole state pickling concept is pretty cool, and kind of throws threads all over..

This is just Multi-core processing...

[mzito]

CMT is nothing more than multi-core processors. Sun is using the marketing idea of CMT to hide the fact that the UltraSparc IV is nothing more than two UltraSparc III cores on one chip.

One way to look at this is Sun maximizing their existing engineering efforts. However, by marketing it as some revolutionary feature advance, they're implying that they've done something new and exciting, as opposed to something that IBM is already doing and AMD and Intel are working on.

Beyond that, Sun and Fujitsu have a co-manufacturing and R&D deal now, confirming something those in the enterprise space have been saying for a long time - Fujitsu was making better Sun servers than Sun.

Plus Sun killed plans for the UltraSparc V, leaving only the Niagra. They have the Opteron line pushing up from below, and rapidly evaporating sales at the high end. They're resorting to marketing gibberish to add new features to the product line, while simultaneously offloading R&D and manufacturing to a partner.

Remind me again why Sun is in the hardware business?

Thanks,
Matt

Re:it means a lot

[leonmergen]

I've learned over the years that preemptive multithreading should be used only as a last resort, and even then, it's best to put exactly one synchronization point in the entire app. Self-contained tasks should be dispatched from that point and deliver their results back with little or no interaction with the other threads.

Exactly, and that's where design patterns come into play... many of these problems have been formally described in patterns you can follow to avoid this; with thread synchronization, you can use the Half-Sync/Half-Async pattern for example, and you can make a task an Active Object so it can deliver its own results...

Multi-Threaded programming is hard, very hard; but you're not alone who thinks it's hard, and many researchers have formally described a bunch of rules you can follow... if you follow these rules, you often enough eliminate most of the more complicated problems.

Re:Hyperthreading

[SunFan]

"Intel has had Hyperthreading available in Pentium 4 and Xeon CPUs for a couple of years now, which does exactly what the article is talking about"

You are wrong. Period. Sun's CMT is several independent CPU cores on the same die with a huge bandwidth interconnect on-die. Intel's Hyperthreading is a gimmicky technology that has a very small real-world impact on performance.

And your personal "benchmarks" cite no numbers. I be trolled!