Настроение:	amused
Entry tags:	computing

MMU makes your CPU 10 times slower
Do you know than the use of MMU incurs 25% performance penalty on memory accesses and greatly complicates CPU designs? So if you throw away MMU, your 16-core CPU could as well be 64-core one. I.e. the actual performance penalty is like 600%!

That is in addition to the extremely expensive switching between the different processes, like asking your OS or GPU driver to do something, or sending message to another process. Also, if there is a real-time process required to run exactly N times per second, like your game's core server, it could be lagging behind a less important processes like some Windows update or telemetry service. So your PUBJ / Counter Strike ping will be lagging, because switching from the telemetry service to your game takes time, and even more time switching from your game to the network packet sending/receiving code. So the real overhead is more like 1000%

The sole reason MMU exists is to limit the technical progress and make you pay them more money, believing in the security theater.

Simpler and efficient no-MMU alternatives:
* Segment bounds checking (i.e. the segmentation fault in the old Unixes).
* Compile time verification (C# and Java code already gets it).

MMU was invented in 80ies when the memory was expensive and RAM was too small, so memory pages could be temporarily unloaded to a swap file. When memories got large enough, the crooks began promoting it as the essential security mechanism, preventing "hackers" from immediately gaining control over OS kernel (which has separate address space). But lets be honest all your important files are inside your Documents folder, and there is little benefit for the hacker to try breaking into kernel. The access scheme is there so you yourself, as user, will be unable to modify you kernel, while Apple/Microsoft/Google will be able to completely control what software you can run.

Zoomers got so detached from history and reality, that they don't know why MMUs were invented. The original Unix ran on a PDP-11, which differs from the pre-i286 x86 only in that it allowed setting segment sizes. That provided the only useful MMU feature at no MMU cost:
http://gunkies.org/wiki/PDP-11_Memory_Management



"Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety." - Benjamin Franklin