- when a process is migrated to a different CPU it may have an active
FPU context in the processor registers. We must save it and migrate
it together with the process.
- any cpu can use smp_schedule() to tell another cpu to reschedule
- if an AP is idle, it turns off timer as there is nothing to
preempt, no need to wakeup just to go back to sleep again
- if a cpu makes a process runnable on an idle cpu, it must wake it up
to reschedule
- tsc_ctr_switch is made cpu local
- although an x86 specific variable it must be declared globaly as the
cpulocal implementation does not allow otherwise
- each CPU has its own runqueues
- processes on BSP are put on the runqueues later after a switch to
the final stack when cpuid works to avoid special cases
- enqueue() and dequeue() use the run queues of the cpu the process is
assigned to
- pick_proc() uses the local run queues
- printing of per-CPU run queues ('2') on serial console
- most global variables carry information which is specific to the
local CPU and each CPU must have its own copy
- cpu local variable must be declared in cpulocal.h between
DECLARE_CPULOCAL_START and DECLARE_CPULOCAL_END markers using
DECLARE_CPULOCAL macro
- to access the cpu local data the provided macros must be used
get_cpu_var(cpu, name)
get_cpu_var_ptr(cpu, name)
get_cpulocal_var(name)
get_cpulocal_var_ptr(name)
- using this macros makes future changes in the implementation
possible
- switching to ELF will make the declaration of cpu local data much
simpler, e.g.
CPULOCAL int blah;
anywhere in the kernel source code
