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While the compiler might be clever enough to consolidate these reads in some cases, the read must happen *somewhere*, which, when we're concerning ourselves with individual instructions, is a very high burden. Instead, cache the `PerCpuPointer` inside the `DynamicPerCpu` structure; then, the `Arc` is used solely to manage the allocation. Signed-off-by: Mitchell Levy --- rust/kernel/percpu.rs | 12 +++++++++--- rust/kernel/percpu/numeric.rs | 2 +- 2 files changed, 10 insertions(+), 4 deletions(-) diff --git a/rust/kernel/percpu.rs b/rust/kernel/percpu.rs index 9659bff2d889..ffcfe02124ab 100644 --- a/rust/kernel/percpu.rs +++ b/rust/kernel/percpu.rs @@ -23,7 +23,10 @@ /// Holds a dynamically-allocated per-CPU variable. pub struct DynamicPerCpu { + // INVARIANT: `ptr` is managed by `alloc` and the value of `ptr` does not change for the + // lifetime of `self`. alloc: Arc>, + ptr: PerCpuPtr, } /// Holds a statically-allocated per-CPU variable. @@ -199,9 +202,10 @@ impl DynamicPerCpu { pub fn new(flags: Flags) -> Option { let alloc: PerCpuAllocation = PerCpuAllocation::new()?; + let ptr = alloc.0; let arc = Arc::new(alloc, flags).ok()?; - Some(Self { alloc: arc }) + Some(Self { alloc: arc, ptr }) } /// Wraps a `PerCpuAllocation` in a `PerCpu` @@ -210,8 +214,9 @@ pub fn new(flags: Flags) -> Option { /// * `alloc` - The allocation to use /// * `flags` - The flags used to allocate an `Arc` that keeps track of the `PerCpuAllocation`. pub fn new_from_allocation(alloc: PerCpuAllocation, flags: Flags) -> Option { + let ptr = alloc.0; let arc = Arc::new(alloc, flags).ok()?; - Some(Self { alloc: arc }) + Some(Self { alloc: arc, ptr }) } } @@ -219,7 +224,7 @@ pub fn new_from_allocation(alloc: PerCpuAllocation, flags: Flags) -> Option PerCpu for DynamicPerCpu { unsafe fn ptr(&mut self) -> &PerCpuPtr { - &self.alloc.0 + &self.ptr } } @@ -227,6 +232,7 @@ impl Clone for DynamicPerCpu { fn clone(&self) -> Self { Self { alloc: self.alloc.clone(), + ptr: self.ptr, } } } diff --git a/rust/kernel/percpu/numeric.rs b/rust/kernel/percpu/numeric.rs index e4008f872af1..1b37cc7e5c19 100644 --- a/rust/kernel/percpu/numeric.rs +++ b/rust/kernel/percpu/numeric.rs @@ -62,7 +62,7 @@ impl DynamicPerCpu<$ty> { /// Returns a `PerCpuNumeric` that can be used to manipulate the underlying per-CPU /// variable. pub fn num(&self) -> PerCpuNumeric<'_, $ty> { - PerCpuNumeric { ptr: &self.alloc.0 } + PerCpuNumeric { ptr: &self.ptr } } } impl StaticPerCpu<$ty> { -- 2.34.1