Multiprocessing

tags : Computer Architecture, Operating Systems, Concurrency

VAS for different architectures §

• 32/64/48 address space, each bit can be 1 or 0, hence $2^{no.ofaddressbits}$. See Permutations & Combinations.
• IA-32/x86_32/x86/i386
  • $2^{32}$ ~= 4GB (32 bit address size)
  • 32 bit machines can still support more ram.(PAE)
• x86_64/amd64
  • $2^{64}$ ~= 18EB (64 bit addresses)
  • 2^{48}^{} ~= 16EB (48 bit addresses)
  • For our use tho, we get only 128TB. Which is not “only” tbf.
  • Why do x86-64 systems have only a 48 bit virtual address space?
  • https://www.kernel.org/doc/Documentation/x86/x86_64/mm.txt

vCPUs §

You always have at least one core, one die and one package.

Name	What
Package	What you get when you buy a single processor. Contains one or more dies.
Die	Actual silicon. A die can contain any number of cores
Socket	The physical connector linking the processor to the computer’s motherboard. There can be multiple.
Core	Independent execution unit that can run one program thread at a time in parallel with other cores.
vCPU	vCPUs are compute threads that process execution for running os/vm.

vCPU calculation §

• (# Sockets) * (# Cores) = (# pCPU) (Physical CPU)
• (# pCPU) * (2 Threads) = (# vCPU) (Virtual CPU)

Thread(s) per core:  2
Core(s) per socket:  4
Socket(s):           1
On-line CPU(s) list:   0-7 (8)

pCPU = 1 * 4 = 4
vCPU = 4*2 = 8

VMs and Hypervisors

Now the term vCPU is widely used in hypervisors etc. In those cases, most hypervisors will let you overprovision cores. That means, you could assign 1 vCPU per VM, but the hypervisors also allow you overcommit every vcpu if you think your workload could handle that.

x86 Microarchitecture levels (march) §

• See x86-64 - Wikipedia
• See x86 Options (Using the GNU Compiler Collection (GCC))
• See x86-64 Microarchitecture Feature Levels
• uops.info
• We can tell compilers about available instruction-set to optimize for using march flag
• These features have to be supported by the CPU in the first place. You can search for your CPU at CPU-World and see supported features.
• Enabled features can be found at cat /proc/cpuinfo
• You can check supported levels with /lib/ld-linux-x86-64.so.2 --help

    x86-64-v4
    x86-64-v3 (supported, searched)
    x86-64-v2 (supported, searched)

• The v2-v4 levels are arbitrary names defined by grouping different instruction sets based on their age and usefulness.

x86-64-baseline §

• CMOV, CMPXCHG8B, FPU, FXSR, MMX, FXSR, SCE, SSE, SSE2

x86-64-v2 §

• CMPXCHG16B, LAHF-SAHF, POPCNT, SSE3, SSE4.1, SSE4.2, SSSE3
• close to Nehalem
• Basically mandatory for modern OS

x86-64-v3 §

• AVX, AVX2, BMI1, BMI2, F16C, FMA, LZCNT, MOVBE, XSAVE
• close to Haswell
• Nice to haves

x86-64-v4 §

• AVX512F, AVX512BW, AVX512CD, AVX512DQ, AVX512VL
• Cutting edge enterprise feature sets

Word §

• See wordsize w $ getconf WORD_BIT and LONG_BIT (32 on my computer)
• WORD (16 bits/2 bytes)
• DWORD (32 bits/4 bytes)
• QWORD (64 bits/8 bytes)

Registers §

Glossary §

Chipset §

• Thing that’s in the motherboard that manages the data flow between the processor, memory and peripherals. i.e I/O Bridge.

Others §

• Clock rate - Wikipedia
• Also see
  • System on module - Wikipedia
  • System on a chip - Wikipedia