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//+private
//+build linux
package time
import linux "core:sys/linux"
_get_tsc_frequency :: proc "contextless" () -> (u64, bool) {
// Get the file descriptor for the perf mapping
perf_attr := linux.Perf_Event_Attr{}
perf_attr.size = size_of(perf_attr)
perf_attr.type = .HARDWARE
perf_attr.config.hw = .INSTRUCTIONS
perf_attr.flags = {.Disabled, .Exclude_Kernel, .Exclude_HV}
fd, perf_errno := linux.perf_event_open(&perf_attr, linux.Pid(0), -1, linux.Fd(-1), {})
if perf_errno != nil {
return 0, false
}
defer linux.close(fd)
// Map it into the memory
page_size : uint = 4096
addr, mmap_errno := linux.mmap(0, page_size, {.READ}, {.SHARED}, fd)
if mmap_errno != nil {
return 0, false
}
defer linux.munmap(addr, page_size)
// Get the frequency from the mapped page
event_page := cast(^linux.Perf_Event_Mmap_Page) addr
if .User_Time not_in event_page.cap.flags {
return 0, false
}
frequency := u64((u128(1_000_000_000) << u128(event_page.time_shift)) / u128(event_page.time_mult))
return frequency, true
}
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