ennowriteallocate

Ennowriteallocate is a configuration option used in computer architecture discussions, simulators, and some documentation to enable a no-write-allocate cache policy for the data cache. When this option is active, a write miss does not bring the corresponding memory block into the cache; instead the write is directed straight to the next memory level or through a write buffer, leaving that block out of the cache.

This policy contrasts with write-allocate, where a write miss loads the block into the cache before performing the write. The ennowriteallocate setting is thus a way to model or enforce a policy where write misses do not pollute the cache with newly written data. In practice, the effect can vary with cache type and memory hierarchy details, such as whether the cache is write-back or write-through and how write buffers are implemented.

Impact on performance and behavior depends on workload. No-write-allocate can reduce cache pollution for workloads with streaming or irregular writes and low data reuse, potentially increasing effective bandwidth by avoiding unnecessary cache fills. However, it can also increase memory traffic and latency for write misses and degrade performance on workloads with good spatial locality or frequent write reuse. The benefits are highly workload dependent and sensitive to the coherence protocol, prefetchers, and buffer strategies in the system.

Implementation notes: in simulators or configurable memory stacks, ennowriteallocate is typically exposed as a boolean flag or policy parameter at the data-cache level. Users enable it to study the effects on hit/mault rates, bandwidth, and energy. It may require careful consideration of coherence and synchronization in multi-core or multi-threaded environments.

See also: Write-allocate, No-write-allocate, Cache memory policies, Write-back, Write-through.