- apic_send_ipi() to send inter-processor interrupts (IPIs)
- APIC IPI schedule and halt handlers to signal x-cpu that a cpu shold
reschedule or halt
- various little changes to let APs run
- no processes are scheduled at the APs and therefore they are idle
except being interrupted by a timer time to time
- 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
- APs configure local timers
- while configuring local APIC timer the CPUs fiddle with the interrupt
handlers. As the interrupt table is shared the BSP must not run
- APs wait until BSP turns paging on, it is not possible to safely
execute any code on APs until we can turn paging on as well as it
must be done synchronously everywhere
- APs turn paging on but do not continue and wait
- to isolate execution inside kernel we use a big kernel lock
implemented as a spinlock
- the lock is acquired asap after entering kernel mode and released as
late as possible. Only one CPU as a time can execute the core kernel
code
- measurement son real hw show that the overhead of this lock is close
to 0% of kernel time for the currnet system
- the overhead of this lock may be as high as 45% of kernel time in
virtual machines depending on the ratio between physical CPUs
available and emulated CPUs. The performance degradation is
significant
- kernel detects CPUs by searching ACPI tables for local apic nodes
- each CPU has its own TSS that points to its own stack. All cpus boot
on the same boot stack (in sequence) but switch to its private stack
as soon as they can.
- final booting code in main() placed in bsp_finish_booting() which is
executed only after the BSP switches to its final stack
- apic functions to send startup interrupts
- assembler functions to handle CPU features not needed for single cpu
mode like memory barries, HT detection etc.
- new files kernel/smp.[ch], kernel/arch/i386/arch_smp.c and
kernel/arch/i386/include/arch_smp.h
- 16-bit trampoline code for the APs. It is executed by each AP after
receiving startup IPIs it brings up the CPUs to 32bit mode and let
them spin in an infinite loop so they don't do any damage.
- implementation of kernel spinlock
- CONFIG_SMP and CONFIG_MAX_CPUS set by the build system
