Linux Synchronization review

UP and SMP

Linux kernel control path

UP vs SMP

API

常見的control path:

ISR

Softirq/tasklet : bh

上面兩個不能context switch

exception/system call :　from user to kernel

setup CR to solve

R/W lock ?

sequence_lock ?

Big Table ?

cpu need HW support for CR

for x86, cmpxchg, compare, exchange

for ARM test_set instruction

CR越小越好

對於singel core, 可以yield cpu,這就要control path必須是一般的path, 而且可以被preempt

從spin_lock進入的時候，kpath要唯一，這樣才不容易死結，不要在中斷中。SMP 要和UP一樣操作。

almost all sync API combine with disable_irq/softirq/preempt_Ex

spin_lock call arch_spin_lock ?

for multicore exclusive instruction, 保證atomic

Read - check - CR (test)

for SMP, LOCK_BREAK is used