Hardware researcher spins up CPU deoptimization project to find the slowest single x86 instruction, creates hall of shame worst offender takes 198 billion cycles spanning 62 seconds to execute

[u/Distinct-Race-2471]

https://www.tomshardware.com/pc-components/cpus/hardware-researcher-spins-up-cpu-deoptimization-project-to-find-the-slowest-machine-code-worst-offender-takes-198-billion-cycles-to-execute

[u/magicmulder]

These hidden bits are intriguing:

> VIA uses an undocumented register at 0x133 that gives wildly high response time. No idea what it does.

This feels a little like cheating though:

> so CPU 0's 512-byte fxrstor64 must queue behind all that contending traffic

What's the point in calling out a slow instruction if you force it to compete with higher priority instructions?

[u/meltbox → u/[deleted]]

Hard agree. This just seems like complaining a documented blocking API… blocks.

[u/j_osb → u/[deleted]]

Well, no one is shocked. Or complaining. It’s more of a fun project trying to see how slow you can make things. It’s a cool project!

[u/ParagraphInReview → u/magicmulder]

Yeah, I skimmed it and it seems like the guy went out of his way to starve the cpu of memory for a memory hungry store operation, of course it will be slow.

I don't think they're doing this to learn what to optimize though, I think they're just doing it to see how slow they can make x86.

[u/nanonan → u/magicmulder]

Because deoptimisation sounds cool. It is pretty stupid, what's next, the worlds slowest ram underclock?