4 ms·
We could have shorter pipelines ;)
by goalieca 8y ago
We could have shorter pipelines ;)
- Filligree 8y agoWhich would hamstring performance.
- goalieca 8y agoyeah. it was a half-joke + half-serious. Would be interesting to see the performance of branch predictor fix vs just having a short pipe.
- titzer 8y agoShorter pipelines don't fundamentally change anything about speculative vulnerabilities. Longer pipelines allow faster clock rates, but that is not the problem here. Speculative vulnerabilities are because branch prediction is needed to get the CPU looking far enough in the future to feed all the functional units so that it can execute not just one instruction per clock, but 4 (actually u-ops, but you get the picture). To do that, you need to know the execution path far into the future. That is not really related to the pipeline depth at all.
- goalieca 8y agoWell yeah, but the implied point is that there must be some depth and workload where having a branch predictor fast or slow makes much less difference.
- trebligdivad 8y agoWell, 'lots of simple cores' is potentially one answer - but it does require you to have the type of workload that can work well heavily threaded. Similarly, CPUs that are heavily threaded rather than speculative, i.e. they don't mind stalling because they have lots of other threads they can switch to.