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in reply to Re^3: Design advice: Classic boss/worker program memory consumption (context switching is cheap)
in thread Design advice: Classic boss/worker program memory consumption

context switching is cheap

Sorry Tye, but that is twaddle. Eiher guesswork, or naiveté.

Firstly, which type of "context switch" are you mis-describing?

The cost of a hardware-based, thread-only context switch runs from 10's to over 1000 microseconds. Add in the need to invalidate and refill L1/L2/L3 caches, and the total time to re-consitute a thread-context back the point that real work can proceed can actually take longer than the maximum timeslice some (flavours of some) OSs will allocate to a thread.

And don't go blaming threads; switching process-contexts is a (collection of) software operations and is more expensive still.

The cost of context switch may come from several aspects. The processor registers need to be saved and restored, the OS kernel code (scheduler) must execute, the TLB entries need to be reloaded, and processor pipeline must be flushed. These costs are directly associated with almost every context switch in a multitasking system. These are the direct costs.

In addition, context switch leads to cache sharing between multiple processes, which may result in performance degradation. This cost varies for different workloads with different memory access behaviors and for different architectures. These are cache interference costs or indirect costs of a context switch


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Re^5: Design advice: Classic boss/worker program memory consumption (cache misses suck)
by tye (Sage) on May 21, 2014 at 03:15 UTC

    Thanks for mostly agreeing with me (despite feeling like you completely disagreed with me).

    - tye        

      Naiveté then. (You headlined your post.)

      Until you show the world how to divorce a "context switch" from "cache misses" -- along with the TLB misses caused by stack segment changes -- your editorialising is not just meaningless, but misinformative ...


      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.