Slashdot Mirror

← Back to Stories (view on slashdot.org)

Not All Cores Are Created Equal

Posted by kdawson on from the working-out-the-kinks dept.

joabj writes "Virginia Tech researchers have found that the performance of programs running on multicore processors can vary from server to server, and even from core to core. Factors such as which core handles interrupts, or which cache holds the needed data can change from run to run. Such resources tend to be allocated arbitrarily now. As a result, program execution times can vary up to 10 percent. The good news is that the VT researchers are working on a library that will recognize inefficient behavior and rearrange things in a more timely fashion." Here is the paper, Asymmetric Interactions in Symmetric Multicore Systems: Analysis, Enhancements and Evaluation (PDF).

4 of 183 comments (clear)

  1. who would've guessed... by Eto_Demerzel79 · · Score: 4, Insightful

    ...programs not designed for multi-core systems don't use them efficiently.

    1. Re:who would've guessed... by timeOday · · Score: 4, Insightful

      No, the programs are not the problem. The programmer should not have to worry about manually assigning processes to cores or switching a process from one core to another - in fact, there's no way the programmer could do that, since it would require knowing what the system load is, what other programs are running, and physical details (such as cache behavior) of processors not even invented yet. This is all the job of the OS.

  2. Re:This isn't news by Clover_Kicker · · Score: 5, Insightful

    80s mainframe tech is NEW and EXCITING to a depressing number of tech people, look at how excited everyone got when someone remembered and re-implemented virtualization.

  3. not a surprise by Eil · · Score: 5, Insightful

    Here's an exercise: Take 2 brand-new systems with identical configurations and start them at the same time doing some job that takes a few hours and utilizes most of the hardware to some significant degree. Say, compiling some huge piece of code like KDE or OpenOffice. System administrators who do exactly this will tell you that you'll almost never see the two machines complete the job at precisely the same time. Even though the CPU, memory, hard drive, motherboard, and everything else is the same, the system as a whole is so complex that minute differences in timing somewhere compound into larger ones. Sometimes you can even reboot them and repeat the experiment and the results will have reversed. It shouldn't come as a surprise that adding more complexity (in the form of processor cores) would enhance the effect.