time: small implementation cleanups #6517
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`StateCell::mark_pending` already uses a loop to retry the compare exchange operation if it fails. The logic within the loop would handle a spurious failure like any other failure, so `compare_exchange_weak` makes the implementation more efficient for some platforms.
This replaces a manual implementation of
`Instant::saturating_duration_since` with the actual one.
Clippy already catches this for primitive integer types via the
`manual_saturating_arithmetic` lint, as demonstrated by the following
example:
```rs
fn saturating_sub(val: usize, n: usize) -> usize {
val.checked_sub(n).unwrap_or(0)
}
```
As explained by the comment removed by this commit earlier Rust versions didn't have an ergonomic way of building arrays of any size of non-Copy types. Rust 1.63 stabilized `array::from_fn`, fixing the above issue and by making it easy to construct arrays from a constructor.
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This replaces `Wheel::levels`, currently represented as a `Vec` of 6 elements, into an array. This should help eliminate some bounds checks from accesses to `levels`. This changes the size of `Wheel` from 48 bytes to 32 bytes on x86_64. The initial implementation didn't Box the array, resulting into `Wheel` having a size of 6264 bytes and loom tests overflowing their stack.
Replaces the manual implementation of a waker list with `WakeList`.
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cc @wathenjiang |
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All LGTM! However, it should be pointed out that in the current implementation, the behavior of I think we should ensure that the order of this FIFO remains unchanged. |
Good catch! I've opened a separate PR to fix it #6521 |
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Order of wakers is generally not something we guarantee, but I think having |
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Motivation
While reading how the timer driver works, I found several things that could be cleaned up.
Solution
I've included those fixes in this PR.