Module single_instr

Extensions for CPU-local types that allows single-instruction operations.

For some per-CPU objects, fetching or modifying the values of them can be done in a single instruction. Then we would avoid turning off interrupts when accessing them, which incurs non-trivial overhead.

These traits are the architecture-specific interface for single-instruction operations. The architecture-specific module can implement these traits for common integer types. For architectures that don’t support such single- instruction operations, we emulate a single-instruction implementation by disabling interruptions and preemptions.

Currently we implement some of the core::ops operations. Bitwise shift implementations are missing. Also for less-fundamental types such as enumerations or boolean types, the caller can cast it themselves to the integer types, for which the operations are implemented.

Safety

All operations in the provided traits are unsafe, and the caller should ensure that the offset is a valid pointer to a static CpuLocalCell object. The offset of the object is relative to the base address of the CPU-local storage. These operations are not atomic. Accessing the same address from multiple CPUs produces undefined behavior.

Traits

SingleInstructionAddAssign

An interface for architecture-specific single-instruction add operation.

SingleInstructionBitAndAssign

An interface for architecture-specific single-instruction bitwise AND.

SingleInstructionBitOrAssign

An interface for architecture-specific single-instruction bitwise OR.

SingleInstructionBitXorAssign

An interface for architecture-specific single-instruction bitwise XOR.

SingleInstructionLoad

An interface for architecture-specific single-instruction get operation.

SingleInstructionStore

An interface for architecture-specific single-instruction set operation.

SingleInstructionSubAssign

An interface for architecture-specific single-instruction subtract operation.