Notes

- Cannot disable interrupt at user level
- Banker algorithm only guarantee safeness of allocating resource. Program can still fail or enters infinite loop
- Strict priority scheduling gives all cpu to high priority threads
- Lock is semaphore with "1"
- In pintos, kernel must fit in 4K page
- Exec() will terminate the existing process and start a new one
- Server listen() once, then accept() multiple times in a loop
- IP only route from machine to machine
- TCP/IP route from port to port
- Fully associated?
- Direct mapped?
- Page fault traps are synchronous exception. Not affected by interrupts
- First level processor cache can prevent correct functioning of memory mapped IO
- OS uses interrupt to register first packet from a bursty network, then use polling to get the rest to avoiding too much overhead.
- Marshalling is the process of gathering argument together for a remote procedure call
- Elevator algorithm is only useful to reduce seeks.
- At user-level, timer interrupt handler will enter scheduler and recover from infinite loop
- Interrupt does not have a thread, therefore it must not sleep
- Threading with user-level package must put all thread to sleep when one thread enter kernel and blocks on I/O
- Too any threads can:
○ Excessive context switch overhead
○ Memory overutilization
○ Excessive synchronization overhead (locks)
- Different tabs in web browser have different source port (TCP/IP) to be uniquely identified
- Kernel mode has:
○ At least one status but to be distinguished from user mode
○ Additional kernel instructions
○ Page marked as kernel mode in PTE only available in kernel mode
○ Control for I/O devices
- SLAB: an allocator customized for one particular object type
○ Reduce internal fragmentation of memory since every object has the same size
○ Reduce objects initialization cost. It can return previously initialized objects to user
- PHYS_BASE is the beginning of kernel virtual memory
- Top half of device driver provide a standardized I/O interface to the rest of kernel. It represent code in which user process can sleep while waiting for I/O
- Bottom half of device driver responds to interrupt from the device and subsequent removal/insertion of information into hardware. Will trigger a wake up of sleeping process as necessary.
- Pinto does not provide equivalent of sbrk() syscall which supports dynamic memory allocation which is used to build malloc().

Address translation:
- Look for segment number if there is one
- Check segment state
- Compare segment size
- Find page entry number
- Segment base + page entry number * entry size
- Check if entry valid or writable
- Repeat for multi-level
- Go straight to physical address