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Anyone have any experience with the control loop one? My uninformed guess is CS people just underestimate the skills and experience to analyze feedback systems

Anyone have any experience with the control loop one? My uninformed guess is CS people just underestimate the skills and experience to analyze feedback systems and so write it off as a bad technology after a poor implementation. Maybe the real problem is you want to know when your system is maxing out the range you anticipated?

avidiax 2y ago
Control theory is an entire discipline. One problem that constantly comes up is ratcheting or poisoning your own inputs. Let's say you want to block "noisy neighbors" from taking large amounts of resources, while allowing all loads to have bursty use of the full system power. Easy, right? Detect the noisy neighbors and throttle them to a small percentage. Unthrottle when they show some substantial idle time. But now, many of those noisy neighbors can't get out of jail because they will, of course, use nearly 100% of their restricted load, even if they would now be well-behaved and merely bursty. There is also a cascading effect, where you have N related bursty loads. One bursts for too long, gets throttled, and now the load is handled by the remaining N-1 loads. But that makes those loads more likely to get throttled, and so on. Only unthrottling all the loads simultaneously will allow them to return to normal bursty operation.
- bobnamob 2y ago
  The fun thing about control theory in CS is that (in my experience) it's far easier to build accurate simulations or even run scaled down experiments than it would be in a physical setting. See articles like [1] or any of Marc Brooker's [2] blog for inspiration [1] https://medium.com/yandex/good-retry-bad-retry-an-incident-story-648072d3cee6 https://medium.com/yandex/good-retry-bad-retry-an-incident-s... [2] https://brooker.co.za/blog/2022/04/11/simulation.html https://brooker.co.za/blog/2022/04/11/simulation.html
- liontwist 2y ago
  > Control theory is an entire discipline. That’s what I said.

avidiax 2y ago

Control theory is an entire discipline. One problem that constantly comes up is ratcheting or poisoning your own inputs. Let's say you want to block "noisy neighbors" from taking large amounts of resources, while allowing all loads to have bursty use of the full system power. Easy, right? Detect the noisy neighbors and throttle them to a small percentage. Unthrottle when they show some substantial idle time. But now, many of those noisy neighbors can't get out of jail because they will, of course, use nearly 100% of their restricted load, even if they would now be well-behaved and merely bursty. There is also a cascading effect, where you have N related bursty loads. One bursts for too long, gets throttled, and now the load is handled by the remaining N-1 loads. But that makes those loads more likely to get throttled, and so on. Only unthrottling all the loads simultaneously will allow them to return to normal bursty operation.

bobnamob 2y ago
The fun thing about control theory in CS is that (in my experience) it's far easier to build accurate simulations or even run scaled down experiments than it would be in a physical setting. See articles like [1] or any of Marc Brooker's [2] blog for inspiration [1] https://medium.com/yandex/good-retry-bad-retry-an-incident-story-648072d3cee6 https://medium.com/yandex/good-retry-bad-retry-an-incident-s... [2] https://brooker.co.za/blog/2022/04/11/simulation.html https://brooker.co.za/blog/2022/04/11/simulation.html
liontwist 2y ago
> Control theory is an entire discipline. That’s what I said.