37 lines
2.0 KiB
Zig
37 lines
2.0 KiB
Zig
//! Kernel tunables — the compile-time knobs, gathered in one place.
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//!
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//! These constants would otherwise be scattered across the files that use them,
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//! hiding the trade-offs. Keeping them here makes them visible at a glance and gives
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//! one spot to change them. They're plain `comptime` constants (zero runtime cost);
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//! any one can later be promoted to a `-D` build option if a target needs to vary it
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//! (see build.zig's `-Dtest-case` for the pattern). This keeps ps2-library.zig to what it
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//! actually is — the bootloader↔kernel handoff *contract* — with tunables living here.
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/// Ceiling on logical CPUs the kernel tracks — the size of the per-CPU bookkeeping
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/// arrays (discovery pool, scheduler state, per-core GDT/TSS). Generous headroom:
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/// those structs are small, and the *large* per-core resources (kernel and IST
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/// stacks) are allocated at bring-up for cores that actually come online, so this
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/// ceiling is cheap. A machine with more logical CPUs has its surplus reported and
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/// left parked (see acpi `cpusDropped`).
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pub const maximum_cpus = 128;
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/// Maximum tasks (kernel threads) alive at once — the static task-table size. Each
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/// online core consumes one slot for its idle task, plus task 0 on the BSP.
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pub const maximum_tasks = 16;
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/// Each task's kernel stack (also each AP's bring-up stack), in bytes.
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pub const kernel_stack_size = 16 * 1024;
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/// Each user process's stack, in pages (32 KiB). Mapped just below a fixed top;
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/// the System V entry block (argc/argv) occupies the top of the highest page, and
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/// the page below the mapping is left unmapped as a guard, so an overflow faults
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/// (killing only that process) instead of silently corrupting the image.
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pub const user_stack_pages = 8;
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/// Each core's IST (double-fault) stack, in bytes. The BSP's is static; an AP's is
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/// heap-allocated at bring-up.
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pub const ist_stack_size = 16 * 1024;
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/// Scheduler tick / preemption rate, in Hz (the timer's periodic frequency).
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pub const timer_hz = 1000;
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