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How to slow down a program and why it can be useful

(stefan-marr.de)
125 points todsacerdoti | 3 comments | 27 Aug 25 11:38 UTC | HN request time: 0s | source
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gwd ◴[27 Aug 25 12:39 UTC] No.45038833[source]▶
Kind of weird that NOP actually slows down the pipeline, as I'd think that would be the easiest thing to optimize out of the pipeline, unless instruction fetch is one of the main limiting factors. Is it architecturally defined that NOP will slow down execution?
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1. IcePic ◴[27 Aug 25 12:55 UTC] No.45039006[source]▶
I think so, as in "make sure all other stuff has run before calling the NOP finished". Otherwise, it would just skip past it and it would have no effect if placed in a loop, so it would be eating memory for no use at all.
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2. bob1029 ◴[27 Aug 25 13:08 UTC] No.45039160[source]▶
Eating memory alone may have the desired effect. The memory bandwidth of a cpu is not infinite.
3. motorest ◴[27 Aug 25 13:21 UTC] No.45039320[source]▶
> I think so, as in "make sure all other stuff has run before calling the NOP finished".

Is this related to speculative execution? The high level description sounds like NOP works as sync points.