Comment by patmorgan23
1 year ago
Not really. RISC-V's benefits are not the "Reduced Instruction Set" part, it's the open ISA part. A small instruction set as actually has several disadvantages. It means you binary bigger because what was a single operation in x86 is now several in RISC-V, meaning more memory bandwidth and cache is taken up by instructions instead of data.
Modern CPUs are actually really good at deciding operations into micro-ops. And the flexibility of being able to implement a complex operation in microcode, or silicon is essential for CPU designers.
Is there a bunch of legacy crap in x86? Yeah. Does getting rid of dramatically increase the performance ceiling? Probably not.
The real benefit of RISC-V is anybody can use it. It's democratizing the ISA. No one has to pay a license to use it, they can just build their CPU design and go.
> Modern CPUs are actually really good at deciding operations into micro-ops.
The largest out-of-order CPUs are actually quite reliant on having high-performance decode that can be performed in parallel using multiple hardware units. Starting from a simplified instruction set with less legacy baggage can be an advantage in this context. RISC-V is also pretty unique among 64-bit RISC ISA's wrt. including compressed instructions support, which gives it code density comparable to x86 at a vastly improved simplicity of decode (For example, it only needs to read a few bits to determine which insns are 16-bit vs. 32-bit length).
> means you binary bigger .... meaning more memory bandwidth and cache
Except this isn't actually true.
> Does getting rid of dramatically increase the performance ceiling? Probably not.
No but it dramatically DECREASES the amount of investment necessary to reach that ceiling.
Assume you have 2 teams, each get the same amount of money. Then ask them to make the highest performing spec compatible chip. What team is gone win 99% of the time?
> And the flexibility of being able to implement a complex operation in microcode, or silicon is essential for CPU designers.
You can add microcode to a RISC-V chip if you want, most people just don't want to.
> The real benefit of RISC-V is anybody can use it.
That is true, but its also just a much better instruction set then x86 -_-
>It means you binary bigger
False premise, as size tool shows RVA20(RV64GC) binaries were already smallest among 64bit architectures.
Code gets smaller still (rather than larger) with newer extensions such as B in RVA22.
As of recently, the same is true in 32bit when comparing rv32 against former best (thumb2). But it was quite close before to begin with.