Performance "speed limits"

By: anon (, June 11, 2019 7:34 pm
Room: Moderated Discussions
Travis Downs ( on June 11, 2019 1:23 am wrote:
> I wrote something about performance speed limits, which is basically a list of things
> that might limit your code (mostly loops) to a specific level of performance. It's
> quantitative, in that it tells you exactly how many iterations/cycle you'll get if
> you hit a particular limit. I've used it in practice and find it effective.
> Have a read if it interests you. Feedback is welcome - I don't have a comments
> system set up* but you could reply here or open an issue on github.

The in-flight branch limit is interesting. It is alleged to be used to roll back architectural state in the case of a mispredict, but of course other operations can cause flushes. Loads and stores of course, likely other rarer machine state changes as well (e.g., some flags bits).

I wonder if Intel attaches some kind of flush / rollback data to every one of these kind of instructions that may cause a flush. Or of the data contained in branch buffer is specifically more detailed and allows faster or more precise recovery as they are the most important case.
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TopicPosted ByDate
Performance "speed limits"Travis Downs2019/06/11 01:23 AM
  Performance "speed limits"Adrian2019/06/11 03:52 AM
    Performance "speed limits"Travis Downs2019/06/11 09:28 AM
  Performance "speed limits"Paul A. Clayton2019/06/11 05:04 AM
    correction of my corrections!Paul A. Clayton2019/06/11 05:07 AM
    Performance "speed limits"Peter E. Fry2019/06/11 07:19 AM
      Performance "speed limits"Travis Downs2019/06/11 09:36 AM
    Performance "speed limits"Travis Downs2019/06/11 09:26 AM
  Performance "speed limits"Branches2019/06/11 08:04 AM
  Performance "speed limits"anon2019/06/11 07:06 PM
    Performance "speed limits"Travis Downs2019/06/11 07:12 PM
      Thank you, very nice writeup (NT)anon2019/06/11 07:37 PM
  Performance "speed limits"anon2019/06/11 07:34 PM
    Performance "speed limits"Maynard Handley2019/06/12 10:13 PM
    Performance "speed limits"Travis Downs2019/06/13 01:05 PM
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