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The enable_interrupts_and_hlt function was renamed to enable_and_hlt

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Philipp Oppermann
2021-02-02 11:09:37 +01:00
parent 00986e8876
commit 6d648457b1
1 changed files with 5 additions and 5 deletions
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10
blog/content/edition-2/posts/12-async-await/index.md
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@@ -1758,9 +1758,9 @@ if self.task_queue.is_empty() {
In case this interrupt pushes to the `task_queue`, we put the CPU to sleep even though there is now a ready task. In the worst case, this could delay the handling of a keyboard interrupt until the next keypress or the next timer interrupt. So how do we prevent it?
The answer is to disable interrupts on the CPU before the check and atomically enable them again together with the `hlt` instruction. This way, all interrupts that happen in between are delayed after the `hlt` instruction so that no wake-ups are missed. To implement this approach, we can use the [`enable_interrupts_and_hlt`] function provided by the [`x86_64`] crate. This function is only available since version 0.9.6, so you might need to update your `x86_64` dependency to use it.
The answer is to disable interrupts on the CPU before the check and atomically enable them again together with the `hlt` instruction. This way, all interrupts that happen in between are delayed after the `hlt` instruction so that no wake-ups are missed. To implement this approach, we can use the [`interrupts::enable_and_hlt`][`enable_and_hlt`] function provided by the [`x86_64`] crate. This function is only available since version 0.9.6, so you might need to update your `x86_64` dependency to use it.
[`enable_interrupts_and_hlt`]: https://docs.rs/x86_64/0.13.2/x86_64/instructions/interrupts/fn.enable_interrupts_and_hlt.html
[`enable_and_hlt`]: https://docs.rs/x86_64/0.13.2/x86_64/instructions/interrupts/fn.enable_and_hlt.html
The updated implementation of our `sleep_if_idle` function looks like this:
@@ -1769,11 +1769,11 @@ The updated implementation of our `sleep_if_idle` function looks like this:
impl Executor {
fn sleep_if_idle(&self) {
use x86_64::instructions::interrupts::{self, enable_interrupts_and_hlt};
use x86_64::instructions::interrupts::{self, enable_and_hlt};
interrupts::disable();
if self.task_queue.is_empty() {
enable_interrupts_and_hlt();
enable_and_hlt();
} else {
interrupts::enable();
}
@@ -1781,7 +1781,7 @@ impl Executor {
}
```
To avoid race conditions, we disable interrupts before checking whether the `task_queue` is empty. If it is, we use the [`enable_interrupts_and_hlt`] function to enable interrupts and put the CPU to sleep as a single atomic operation. In case the queue is no longer empty, it means that an interrupt woke a task after `run_ready_tasks` returned. In that case, we enable interrupts again and directly continue execution without executing `hlt`.
To avoid race conditions, we disable interrupts before checking whether the `task_queue` is empty. If it is, we use the [`enable_and_hlt`] function to enable interrupts and put the CPU to sleep as a single atomic operation. In case the queue is no longer empty, it means that an interrupt woke a task after `run_ready_tasks` returned. In that case, we enable interrupts again and directly continue execution without executing `hlt`.
Now our executor properly puts the CPU to sleep when there is nothing to do. We can see that the QEMU process has a much lower CPU utilization when we run our kernel using `cargo run` again.