Intel provides nice schematic diagrams of the layouts of their processor chips, but provides no guidance on how the user-visible core numbers and L3 slice numbers map to the locations on the die. Most of the time there is no “need” to know the locations of the units, but there… read more
Performance Counters
SC18 paper: HPL and DGEMM performance variability on Intel Xeon Platinum 8160 processors
Here are the annotated slides from my SC18 presentation on Snoop Filter Conflicts that cause performance variability in HPL and DGEMM on the Xeon Platinum 8160 processor. This slide presentation includes data (not included in the paper) showing that Snoop Filter Conflicts occur in all Intel Scalable Processors (a.k.a., “Skylake… read more
Using hardware performance counters to determine how often both logical processors are active on an Intel CPU
Most Intel microprocessors support “HyperThreading” (Intel’s trademark for their implementation of “simultaneous multithreading”) — which allows the hardware to support (typically) two “Logical Processors” for each physical core. Processes running on the two Logical Processors share most of the processor resources (particularly caches and execution units). Some workloads (particularly heterogeneous… read more