begin adding tsc frequency getters

core/time/perf.odin

@@ -1,6 +1,7 @@
 package time
 
 import "core:runtime"
+import "core:intrinsics"
 
 Tick :: struct {
 	_nsec: i64, // relative amount
@@ -40,6 +41,26 @@ _tick_duration_end :: proc "contextless" (d: ^Duration, t: Tick) {
 	d^ = tick_since(t)
 }
 
+when ODIN_ARCH == .amd64 {
+	_has_invariant_tsc :: proc "contextless" () -> bool {
+		eax, _, _, _ := intrinsics.x86_cpuid(0x80_000_000, 0)
+
+		// Is this processor *really* ancient?
+		if eax < 0x80_000_007 {
+			return false
+		}
+
+		// check if the invariant TSC bit is set
+		_, _, _, edx := intrinsics.x86_cpuid(0x80_000_007, 0)
+		return (edx & (1 << 8)) != 0
+
+	}
+} else {
+	_has_invariant_tsc :: proc "contextless" () -> bool {
+		return false
+	}
+}
+
 /*
 	Benchmark helpers
 */
@@ -94,4 +115,4 @@ benchmark :: proc(options: ^Benchmark_Options, allocator := context.allocator) -
 		options->teardown(allocator) or_return
 	}
 	return
-}
+}

core/time/tsc_linux.odin

@@ -0,0 +1,43 @@
+//+private
+//+build linux
+package time
+
+import "core:intrinsics"
+import "core:sys/unix"
+
+_get_tsc_frequency :: proc "contextless" () -> u64 {
+	@(static) frequency : u64 = 0
+	if frequency > 0 {
+		return frequency
+	}
+
+	perf_attr := unix.Perf_Event_Attr{}
+	perf_attr.type = u32(unix.Perf_Type_Id.Hardware)
+	perf_attr.config = u64(unix.Perf_Hardware_Id.Instructions)
+	perf_attr.size = size_of(perf_attr)
+	perf_attr.flags = {.Disabled, .Exclude_Kernel, .Exclude_HV}
+	fd := unix.sys_perf_event_open(&perf_attr, 0, -1, -1, 0)
+	if fd == -1 {
+		frequency = 1
+		return 0
+	}
+	defer unix.sys_close(fd)
+
+	page_size : uint = 4096
+	ret := unix.sys_mmap(nil, page_size, unix.PROT_READ, unix.MAP_SHARED, fd, 0)
+	if ret == unix.MAP_FAILED {
+		frequency = 1
+		return 0
+	}
+	addr := rawptr(uintptr(ret))
+	defer unix.sys_munmap(addr, page_size)
+
+	event_page := (^unix.Perf_Event_mmap_Page)(addr)
+	if .User_Time not_in event_page.cap.flags {
+		frequency = 1
+		return 0
+	}
+
+	frequency = u64((u128(1_000_000_000) << u128(event_page.time_shift)) / u128(event_page.time_mult))
+	return frequency
+}