cpu

Tags: computers

• https://travisdowns.github.io/blog/2021/06/17/rip-zero-opt.html

Registers

• Nowadays, all registers can be used as general purpose registers
• RBP is used as a general purpose one, with RSP taking the role as a frame pointer. RIP is still in the stack memory region for each function call
• info registers in gdb
• Constants are encoded in instructions, but arbitrary values are retrieved from memory
• Goto is a JMP
• Function calls are CALL
• When a function is called from a caller, the callee needs to make room for local variables. In 64bit x86, usually the first six arguments are passed in registers
• Then it saves the base pointer into RBP, and then sets up the new base ptr

Cache Lines

• https://lore.kernel.org/netdev/20231129072756.3684495-2-lixiaoyan@google.com/
  • Aligning structs in TCP gives a ton of improvements!

Types of Caches

Direct Mapped Cache

• Like consistent hashing, each memory address is used to map a block to a specific cache line
• both provide deterministic mapping

Fully Associative Cache

• Memory can be stored in any cache line, but we need to search to find it

Set Associative

• Memory address is used to determine the set, and the data can be placed in any block within the set

Load-Linked and Store-Conditional (LL/SC)

• Pair of instructions used in concurrent programming
• Achieves syncronization without locks
• Load-Linked - reads the current value from memory location and “links” it, typically by marking the address in a special way within the processor
• Store-Conditional - attempts to write a new value to the memory location that was read by LL. Write will only succeed if the location has not been udpated since LL was executed