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What's new in CPUs since the 80s and how does it affect programmers?

danluu.com

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Re: What's new in CPUs since the 80s and how does it affect programmers?

#21

Post by ansible »

What interested me in the design of the Mill CPU is how it throws out the usual design of machine language.

I'm not talking about assembly language, and I know the difference, BTW.

In the name of software compatibility, we're still trying to program CPUs using machine language that wouldn't be so strange to a programmer from the 1980's. Sure, there's more registers, and some fun new stuff, but it isn't all that different.

Except that in the 1980's, the CPU actually implemented those instructions. These days, it is all a lie, especially with regards to things like register sets and aliasing. Yes, of course, logically, what the programmer wanted to happen does, but today even programming at assembly level, you are far, far removed from what the CPU is actually doing.

Edit: Here's the website: http://millcomputing.com/docs/

Re: What's new in CPUs since the 80s and how does it affect programmers?

#22

Post by dang »

detaro wrote: post #3
mgrennan wrote: post #2

This is a wonderful post that no-one will care about. This may be the only post. Today, programmers are more interested in the rate they can turn out "Just Works" code. These kinds of details are fare fare to down in the weeds for a continuous development artists.

> This is a wonderful post that no-one will care about. This may be the only post. I think you are underestimating the crowd here. Last time it was posted it got quite a few responses: https://news.ycombinator.com/item?id=8873250 (already a while back, but might be interesting for reference/to bring topics up again)

Seven months ago is well within duplicate range, but let's leave this one up: first to show how much the HN community does care about wonderful posts, and second to thank luu for tirelessly posting (not to mention writing) so many high-quality articles here.

If any of you want to see an example of how much difference a single user can make to HN, look at https://news.ycombinator.com/submitted?id=luu. Thank you, Dan!

Re: What's new in CPUs since the 80s and how does it affect programmers?

#23

Post by dang »

ansible wrote: post #21

What interested me in the design of the Mill CPU is how it throws out the usual design of machine language. I'm not talking about assembly language, and I know the difference, BTW. In the name of software compatibility, we're still trying to program CPUs using machine language that wouldn't be so strange to a programmer from the 1980's. Sure, there's more registers, and some fun new stuff, but it isn't all that diffe…

> how it throws out the usual design of machine language

Now I'm curious. How does it?

Re: What's new in CPUs since the 80s and how does it affect programmers?

#24

Post by chipsy »

fiatmoney wrote: post #5

It's strange the extent to which programming interview questions reflect an 80s view of the cost of operations, particularly the overabundance of linked list and binary tree questions. Cache misses ain't free and memory scans are relatively cheap after you do the initial lookup.

I think most such interview questions are informed by CS curricula, which also have only changed modestly since 1980(some new languages and tools). The elaborate pointer chasing structures available then have basically sufficed and are in many instances less useful new.

Re: What's new in CPUs since the 80s and how does it affect programmers?

#25

Post by dang »

mgrennan wrote: post #2

This is a wonderful post that no-one will care about. This may be the only post. Today, programmers are more interested in the rate they can turn out "Just Works" code. These kinds of details are fare fare to down in the weeds for a continuous development artists.

All: I had a negative reaction to this comment too at first, but on reflection it reads less like a jab and more like a rueful lament about mainstream programming culture. The fact that mgrennan loved the article and was so perfectly wrong about it not being appreciated here suggests that he or she just hasn't realized yet how much passion this community shares for the craft.

It's depressing to feel like you're the only one who cares, and when one has felt like that for a long time, curmudgeonly biases develop. So mgrennan, please get to know your fellow HNers, who love this stuff. And HN, let's be charitable to mgrennan, who may have been mistaken but whose heart is probably in the right place.

Re: What's new in CPUs since the 80s and how does it affect programmers?

#26

Post by w0000t »

dang wrote: post #23
ansible wrote: post #21

What interested me in the design of the Mill CPU is how it throws out the usual design of machine language. I'm not talking about assembly language, and I know the difference, BTW. In the name of software compatibility, we're still trying to program CPUs using machine language that wouldn't be so strange to a programmer from the 1980's. Sure, there's more registers, and some fun new stuff, but it isn't all that diffe…

> how it throws out the usual design of machine language Now I'm curious. How does it?

No ordinary registers. Instead you have a FIFO queue( belt ), where every element( register ) is accessible and has a relative address( offset ).

https://www.youtube.com/watch?v=QGw-cy0ylCc&list=PLFls3Q5bBI...

Re: What's new in CPUs since the 80s and how does it affect programmers?

#27

Post by trsohmers »

fiatmoney wrote: post #5

It's strange the extent to which programming interview questions reflect an 80s view of the cost of operations, particularly the overabundance of linked list and binary tree questions. Cache misses ain't free and memory scans are relatively cheap after you do the initial lookup.

Yep! The big thing people don't realize that it is memory operations that are the biggest cost in terms of both time and energy.

While it takes ~100 picojoules to do a double precision floating point operation on a Ivy Bridge Intel processor, it takes 4200 picojoules to move the 64 bits from DRAM to your registers. Most people assume that the huge power usage is because you need to move data from off the chip, but the reality (and surprising fact to most people) is that over 60% (~2500 picojoules) of the energy usage of moving the data is consumed by the on chip cache hierarchy. That doesn't mean the SRAM caches themselves, but all the additional logic that makes it hardware managed (TLBs, etc) that give you functionality like virtual memory translations, cache coherency, etc.

Getting rid of all of that cruft that has been added since the 80s to make programmers lives easier would actually reduce power consumption and latency significantly... My startup is working on that problem by removing all of that additional logic from the hardware and instead having it managed at compile time. The best thing though would be having programmers really think about locality when writing their programs though.

Re: What's new in CPUs since the 80s and how does it affect programmers?

#28

Post by gizmo686 »

ansible wrote: post #21

What interested me in the design of the Mill CPU is how it throws out the usual design of machine language. I'm not talking about assembly language, and I know the difference, BTW. In the name of software compatibility, we're still trying to program CPUs using machine language that wouldn't be so strange to a programmer from the 1980's. Sure, there's more registers, and some fun new stuff, but it isn't all that diffe…

It is worth noting that many of the Mill features are also a "lie" (for example, the belt is still just registers and register renaming). Its just that the Mill uses lies designed for modern processor technology.

Re: What's new in CPUs since the 80s and how does it affect programmers?

#29

Post by w0000t »

gizmo686 wrote: post #28
ansible wrote: post #21

What interested me in the design of the Mill CPU is how it throws out the usual design of machine language. I'm not talking about assembly language, and I know the difference, BTW. In the name of software compatibility, we're still trying to program CPUs using machine language that wouldn't be so strange to a programmer from the 1980's. Sure, there's more registers, and some fun new stuff, but it isn't all that diffe…

It is worth noting that many of the Mill features are also a "lie" (for example, the belt is still just registers and register renaming). Its just that the Mill uses lies designed for modern processor technology.

False. Mill does not do register renaming. ( Or use "lies". I failed to comprehend you second sentence. )

Here is a talk from one of the designers explaining how it is done: https://www.youtube.com/watch?v=QGw-cy0ylCc&feature=youtu.be...

Re: What's new in CPUs since the 80s and how does it affect programmers?

#30

Post by shadowfox »

trsohmers wrote: post #27
fiatmoney wrote: post #5

It's strange the extent to which programming interview questions reflect an 80s view of the cost of operations, particularly the overabundance of linked list and binary tree questions. Cache misses ain't free and memory scans are relatively cheap after you do the initial lookup.

Yep! The big thing people don't realize that it is memory operations that are the biggest cost in terms of both time and energy. While it takes ~100 picojoules to do a double precision floating point operation on a Ivy Bridge Intel processor, it takes 4200 picojoules to move the 64 bits from DRAM to your registers. Most people assume that the huge power usage is because you need to move data from off the chip, but th…

> My startup is working on that problem by removing all of that additional logic from the hardware and instead having it managed at compile time.

Maybe a naive question. How do you foresee your approach with this succeeding given the failure of Itanium's similar approach?

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