[salawat]

Speculative exec ruins everything again.

I get the performance gainz, but when are we going to get past the formal fallacy that executing any instruction we don't need to based on actual flow is de facto a complete violation of user expectations and therefore completely unsafe to do.

Like every lay person I explain speculative execution seems to be able to recognize that a pipeline stall to figure out what a value actually is just the way to go.

Hell, my personal sanity check with computing is that there must exist a humans only implementation that correlates to a good computing primitive.

Nowhere on Earth, will you find an organization that will execute both sides of a conditional process requiring hunans to do the work just to throw away the result. Not taken.

Oh wait... Finance does it with Hedges...

Frigging finance. Ruins everything for everyone.

[avianes]

> Nowhere on Earth, will you find an organization that will execute both sides of a conditional process requiring hunans to do the work just to throw away the result. Not taken.

Speculative execution today (within modern high-end processor) does not execute both sides of a conditional branch.

It would indeed be a waste of power and it would be a much more complex micro-architecture.

Modern speculative OoO processors execute a single path and simply relies on the branch predictor accuracy. And they are pretty accurate, on the order of 3 misspredictions every 1000 instructions. The power consumption in unnecessary work due to a missprediction is quite low.

Modern processors consume much of their power in Out-of-Order instruction scheduling.

[salawat]

Looks like I need to go through Patterson and Hennessy again.

As I was fairly sure that as many computations were done as possible in the same cycle with the ditching of "not the case" results on subbsequent cycles, but I'll be the first to admit I haven't synced on the bleeding edge lit recently. And sipping power has become much more of a concern in recent years, do I may be due for a refresh anyway.

My favorite past time if the statistics are to be believed.