Glossary/CPU/Multi-core scaling

Multi-core scaling

Multi-core scaling is how close a workload gets to N-times speedup on N cores, limited by serial code, shared cache, memory bandwidth, and clock drop.

Also known as parallel scaling, core scaling

Measured by SystemCheck

Part of the four-stage run: a 60-second sustained CPU load reporting throughput, decay and consistency; a memory stage reporting bandwidth and latency; a calibrated GPU raster load reporting frame time, pacing and decay; and a path tracer reporting samples per second. The paragraphs below say which metric carries this term.

Perfect scaling is unreachable. Amdahl's law caps you at the serial fraction of the work; below that, four practical effects erode the rest: all-core boost is lower than single-core boost, cores contend for shared L3 and memory bandwidth, SMT threads share execution resources, and synchronisation costs grow with thread count.

Observed scaling on a healthy desktop for a compute-bound parallel workload is typically 60-85% of theoretical. Much below that on a workload that should parallelise cleanly points at a real constraint: memory bandwidth saturation, an aggressive power limit that collapses all-core clocks, or background processes stealing cores.

SystemCheck's CPU stage saturates every logical processor with independent Web Worker tasks, which is close to an ideal parallel workload. If your multi-core result is far below what your core count suggests relative to comparable machines, the bottleneck is in your system, not in the code being run.

Related terms

All-core boostAll-core boost is the frequency a CPU holds when every core is loaded, always lower than the single-core boost clock because power and heat scale with active cores.Read more Core vs threadA core is a physical execution unit; a thread is a logical stream of work, and one core can expose two threads via simultaneous multithreading.Read more SMT / Hyper-ThreadingSMT lets one physical core run two instruction streams at once, using execution units that would otherwise sit idle while a thread waits on memory.Read more Memory bandwidthMemory bandwidth is the rate at which data moves between the CPU and system RAM, limiting workloads whose data does not fit in cache.Read more Single-core performanceSingle-core performance is how much work one CPU core completes on its own, and it governs responsiveness in games and most interactive software.Read more

Run the free test All terms