diff options
Diffstat (limited to 'boot/sched.zig')
| -rw-r--r-- | boot/sched.zig | 23 |
1 files changed, 9 insertions, 14 deletions
diff --git a/boot/sched.zig b/boot/sched.zig index 95b94e0..60a8fa0 100644 --- a/boot/sched.zig +++ b/boot/sched.zig @@ -1,22 +1,14 @@ -// tiny preemptive round robin scheduler -// -// every schedulable thing is a task holding a saved register frame + its cr3 -// task 0 is the kernel itself (the event loop / shell), always ready. the pit -// tick (idt.zig -> tick) is where we preempt: save the interrupted tasks frame, -// pick the next ready task, copy its frame back over the one on the stack, and -// the irq return path iretqs straight into it. iretq handles ring 0 <-> ring 3 -// the same way (long mode always restores ss:rsp), so one swap covers leaving -// either the kernel or a process -// -// each user task gets its own kernel stack (for its ring3->ring0 syscall/irq -// entries) and we point tss.rsp0 at it on switch. thats what keeps preempting a -// task mid syscall safe (e.g. read()s sti+hlt). a shared rsp0 would get -// clobbered the next time any task trapped into the kernel +// tiny preemptive round robin scheduler. a task is a saved frame + cr3 + kernel +// stack, task 0 is the kernel event loop. the pit tick swaps the interrupted +// frame for the next ready tasks and iretqs in, which covers ring 0 and ring 3 +// alike. each task has its own kernel stack so preempting one mid syscall (e.g. a +// read() parked on sti/hlt) doesnt clobber anothers rsp0 const std = @import("std"); const Frame = @import("regs.zig").Frame; const vmm = @import("vmm.zig"); const gdt = @import("gdt.zig"); +const bridge = @import("bridge"); const MAX_TASKS = 8; const KSTACK_SIZE = 16 * 1024; @@ -156,6 +148,9 @@ pub fn deliverInput(byte: u8) bool { // the preemption point, called from the pit irq with the interrupted frame pub fn tick(frame: *Frame) void { + // dont preempt task 0 mid vm call, the shared fiber cant be re-entered + if (bridge.vmBusy()) return; + if (tasks[current].state == .dead) { tasks[current].state = .free; // reclaim, dont bother saving its context } else if (tasks[current].state == .blocked) { |