A Case Against (Most) Context Switches

By: Andrey (andrey.semashev.delete@this.gmail.com), May 18, 2021 6:58 am
Room: Moderated Discussions
Little Horn (sink.delete@this.example.net) on May 17, 2021 5:03 pm wrote:
> Thoughts?

The proposed design seems to largely assume that all runnable threads are actually being executed by the CPU. I feel that this assumption is not practical, as there will certainly be the case when there are more tasks that can run than the CPU can handle.

When that happens, the proposal doesn't explain some important points:

- How does the hardware monitor addresses that are waited by threads that don't fit in the CPU capabilities? Surely, the CPU can't fetch this information from RAM on every memory access (by the CPU or other bus agents) as that would tank performance.

- More threads than the CPU can execute means thread preemption must exist, with a thread scheduler and context switching overhead that is likely close to what we have now. And at this point, is this model much better than the current software scheduling design running on a high thread count CPU? I suspect the hardware-accelerated thread scheduling could be beneficial, but not to the amount the paper tries to suggest.
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TopicPosted ByDate
A Case Against (Most) Context SwitchesLittle Horn2021/05/17 05:03 PM
  A Case Against (Most) Context Switchesrwessel2021/05/17 06:55 PM
  A Case Against (Most) Context SwitchesFoo_2021/05/18 01:58 AM
    A Case Against (Most) Context SwitchesDoug S2021/05/18 08:45 AM
      A Case Against (Most) Context SwitchesKonrad Schwarz2021/05/19 07:35 AM
  A Case Against (Most) Context SwitchesEtienne Lorrain2021/05/18 03:11 AM
  A Case Against (Most) Context SwitchesAndrey2021/05/18 06:58 AM
  A Case Against (Most) Context Switchesgallier22021/05/18 08:41 AM
  A Case Against (Most) Context Switches---2021/05/18 09:00 AM
  A Case Against That Other PaperBrendan2021/05/18 12:37 PM
    A Case Against That Other PaperMark Roulo2021/05/18 03:32 PM
      A Case Against That Other PaperBrendan2021/05/18 11:05 PM
        A Case Against That Other PaperMark Roulo2021/05/19 01:09 PM
  A Case Against (Most) Context SwitchesRomain Dolbeau2021/05/19 04:05 AM
    A Case Against (Most) Context SwitchesBjörn Ragnar Björnsson2021/05/19 01:13 PM
      A Case Against ... authors show zero awareness of Cray-MTABjörn Ragnar Björnsson2021/05/19 06:18 PM
    Cray MTA avoided cachesPaul A. Clayton2021/05/20 06:36 AM
      Cray MTA avoided cachesdmcq2021/05/20 10:09 AM
        Cray MTA avoided cachesRayla2021/05/20 10:28 AM
      A LONG response to the paperPaul A. Clayton2021/05/22 06:15 AM
        A LONG response to the paperAdrian2021/05/22 09:18 AM
          Thank you for the note of appreciationPaul A. Clayton2021/05/24 05:06 AM
  A Case Against (Most) Context Switchesdmcq2021/05/19 01:47 PM
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