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fix(platform/timer): on x86_64, elide usage of asm!() and use _rdtsc() intrinsic

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This commit is contained in:
Alex Zenla
2025-11-03 02:57:22 -05:00
parent be63c5171b
commit ba634ed68a
3 changed files with 8 additions and 55 deletions
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4
crates/sprout/src/platform/timer.rs
View File

@@ -17,7 +17,7 @@ pub enum TickFrequency {
/// The platform provides the tick frequency.
Hardware(u64),
/// The tick frequency is measured internally.
Measured(u64, Duration),
Measured(u64),
}
impl TickFrequency {
@@ -25,7 +25,7 @@ impl TickFrequency {
fn ticks(&self) -> u64 {
match self {
TickFrequency::Hardware(frequency) => *frequency,
TickFrequency::Measured(frequency, _) => *frequency,
TickFrequency::Measured(frequency) => *frequency,
}
}

10
crates/sprout/src/platform/timer/aarch64.rs
View File

@@ -10,16 +10,6 @@ pub fn ticks() -> u64 {
counter
}
/// We can use the actual ticks value as our start value.
pub fn start() -> u64 {
ticks()
}
/// We can use the actual ticks value as our stop value.
pub fn stop() -> u64 {
ticks()
}
/// Our frequency is provided by cntfrq_el0 on the platform.
pub fn frequency() -> TickFrequency {
let frequency: u64;

49
crates/sprout/src/platform/timer/x86_64.rs
View File

@@ -1,5 +1,4 @@
use crate::platform::timer::TickFrequency;
use core::arch::asm;
use core::time::Duration;
/// We will measure the frequency of the timer based on 1000 microseconds.
@@ -8,52 +7,16 @@ const MEASURE_FREQUENCY_DURATION: Duration = Duration::from_micros(1000);
/// Read the number of ticks from the platform timer.
pub fn ticks() -> u64 {
let mut eax: u32;
let mut edx: u32;
unsafe {
asm!("rdtsc", out("eax") eax, out("edx") edx);
}
(edx as u64) << 32 | eax as u64
}
/// Read the starting number of ticks from the platform timer.
pub fn start() -> u64 {
let rax: u64;
unsafe {
asm!(
"mfence",
"lfence",
"rdtsc",
"shl rdx, 32",
"or rax, rdx",
out("rax") rax
);
}
rax
}
/// Read the ending number of ticks from the platform timer.
pub fn stop() -> u64 {
let rax: u64;
unsafe {
asm!(
"rdtsc",
"lfence",
"shl rdx, 32",
"or rax, rdx",
out("rax") rax
);
}
rax
// SAFETY: Reads the platform timer, which is safe in any context.
unsafe { core::arch::x86_64::_rdtsc() }
}
/// Measure the frequency of the platform timer.
/// NOTE: Intentionally, we do not synchronize rdtsc during measurement to match systemd behavior.
fn measure_frequency() -> u64 {
let start = start();
let start = ticks();
uefi::boot::stall(MEASURE_FREQUENCY_DURATION);
let stop = stop();
let stop = ticks();
let elapsed = stop.wrapping_sub(start) as f64;
(elapsed / MEASURE_FREQUENCY_DURATION.as_secs_f64()) as u64
}
@@ -62,5 +25,5 @@ fn measure_frequency() -> u64 {
/// On x86_64, this is slightly expensive, so it should be done once.
pub fn frequency() -> TickFrequency {
let frequency = measure_frequency();
TickFrequency::Measured(frequency, MEASURE_FREQUENCY_DURATION)
TickFrequency::Measured(frequency)
}