parallel computing and the os

Minicomputers -> after timesharing
- parallel computing sort of dropped off with this
- logs and interrupts
- multiprocess parallelism sort of died
client/server computing make IO concurrcy big
- must exploit I/O concurrency
- microkernel organizations
  - User level services for I/O -> moves into microkernels, pthreads standard
events vs threads
- no sharing of handlers, no locks, etc, CSP style
  - most webservers today are events style
  - john usterhat
multiprocessors make a return, NUMA stuff becomes big again
- but uniprocessors performance keeps improving
multicore processors come roaring back
- cores per processor increase yet again performance goes back up
- moore’s law is dead on single cores, but multi cores are back
- make, for example, increases and scale more
  - reading a cache line from a different core is expensive
  - congestion on cache lines, but avoiding cache line sharing is challenging
    - even a RW lock is expensive
    - basically the only real optimization is to stop spraying your data structures everywhere
  - RCU!
    - writers must follow careful discipline
phase 4? OS community? Commmodity chips? -> Cloud computing, map reduce, moving data is expensive, move compute
- shared memory locks have gotten better!
- parallelism ahs moved up the software stack driven by commodity hardware