add test to determine the TSC frequency

src/vm.rs

@@ -811,11 +811,97 @@ fn get_cpu_frequency_from_os() -> std::result::Result<u32, ()> {
 
 #[cfg(test)]
 mod tests {
+	const MHZ_TO_HZ: u64 = 1000000;
+	const KHZ_TO_HZ: u64 = 1000;
+
 	#[cfg(target_os = "linux")]
 	use crate::linux::tests::has_vm_support;
+	#[cfg(target_arch = "x86_64")]
+	use core::arch::x86_64::_rdtsc as rdtsc;
+	use std::time;
 
 	use super::*;
 
+	#[test]
+	fn test_detect_freq_from_cpuid() {
+		let cpuid = CpuId::new();
+		let has_tsc = cpuid
+			.get_feature_info()
+			.map_or(false, |finfo| finfo.has_tsc());
+
+		let has_invariant_tsc = cpuid
+			.get_extended_function_info()
+			.map_or(false, |efinfo| efinfo.has_invariant_tsc());
+
+		let tsc_frequency_hz = cpuid.get_tsc_info().map(|tinfo| {
+			if tinfo.nominal_frequency() != 0 {
+				tinfo.tsc_frequency()
+			} else if tinfo.numerator() != 0 && tinfo.denominator() != 0 {
+				// Skylake and Kabylake don't report the crystal clock, approximate with base frequency:
+				cpuid
+					.get_processor_frequency_info()
+					.map(|pinfo| pinfo.processor_base_frequency() as u64 * MHZ_TO_HZ)
+					.map(|cpu_base_freq_hz| {
+						let crystal_hz = cpu_base_freq_hz * tinfo.denominator() as u64
+							/ tinfo.numerator() as u64;
+						crystal_hz * tinfo.numerator() as u64 / tinfo.denominator() as u64
+					})
+			} else {
+				None
+			}
+		});
+
+		if has_tsc {
+			// Try to figure out TSC frequency with CPUID
+			println!(
+				"TSC Frequency is: {} ({})",
+				match tsc_frequency_hz {
+					Some(x) => format!("{} Hz", x.unwrap_or(0)),
+					None => String::from("unknown"),
+				},
+				if has_invariant_tsc {
+					"invariant"
+				} else {
+					"TSC frequency varies with speed-stepping"
+				}
+			);
+
+			// Check if we run in a VM and the hypervisor can give us the TSC frequency
+			cpuid.get_hypervisor_info().map(|hv| {
+				hv.tsc_frequency().map(|tsc_khz| {
+					let virtual_tsc_frequency_hz = tsc_khz as u64 * KHZ_TO_HZ;
+					println!(
+						"Hypervisor reports TSC Frequency at: {} Hz",
+						virtual_tsc_frequency_hz
+					);
+				})
+			});
+
+			// Determine TSC frequency by measuring it (loop for a second, record ticks)
+			let one_second = time::Duration::from_secs(1);
+			let now = time::Instant::now();
+			let start = unsafe { rdtsc() };
+			if start > 0 {
+				loop {
+					if now.elapsed() >= one_second {
+						break;
+					}
+				}
+				let end = unsafe { rdtsc() };
+				println!(
+					"Empirical measurement of TSC frequency was: {} Hz",
+					(end - start)
+				);
+			} else {
+				println!("Don't have rdtsc on stable!");
+				assert!(true);
+			}
+		} else {
+			println!("System does not have a TSC.");
+			assert!(true);
+		}
+	}
+
 	#[cfg(target_os = "linux")]
 	#[test]
 	fn test_get_cpu_frequency_from_os() {