xPU pipeline microarch

xPU pipeline overview

insn define

item	feature
Dimension	scalar / vector
insn	alu / shift / logic / load-store / control / csr

Pipeline

example

1. simple pipeline

2. complex pipeline

3. mulit-issue pipeline

4. SIMT pipeline

define

1. 使用buffer解耦
2. 不同长度的pipeline
3. 反馈导致pipeline阻塞

status

1. forward
2. stall

control/operate

1. drain off

2. cutoff

3. back pressure

4. flush

5. Speculative execution

6. buffer read/write

level

pipeline	feature
order 5 stage	IF,Decode,EXE,MEM,WB
order multi-issue	multi pipeline, frondEnd/backEnd
OoO	out-of-order execute, multi-issue
multi-thread	order, multi-thread; OoO,multi-issue, multi-thread
SIMT	SIMD, multi-thread

insn mapping

1. pipeline stage
2. key data structure

performance

1. buffer可将流水线解耦
2. 流水线中，各阶段的流量都等于起始的流量则性能达到最佳(后续流水线没有阻塞/断流)
3. 上述特性可用于xPU的流水线性能分析
4. referecen method: TMAT-Top-Down performance analysis methodology

思考

1. pipeline中能使用状态机吗?
2. pipeline中如何valid-ready控制流水线的阻塞/反压?

reference

1. 流水线中的valid-ready握手控制打拍
2. 数字芯片设计——握手与反压
3. 流水线设计中的反压操作