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. 不同長度的pipeline
3. 反饋導致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可將流水線解耦
2. 流水線中，各階段的流量都等於起始的流量則性能達到最佳(後續流水線沒有阻塞/斷流)
3. 上述特性可用於xPU的流水線性能分析
4. referecen method: TMAT-Top-Down performance analysis methodology

思考

1. pipeline中能使用狀態機嗎?
2. pipeline中如何valid-ready控制流水線的阻塞/反壓?

reference

1. 流水線中的valid-ready握手控制打拍
2. 數字芯片設計——握手與反壓
3. 流水線設計中的反壓操作