Continuous in-memory accumulation of hardware performance counter data

In-memory accumulation of hardware counts in a computer system is carried out by continuously sending count values from full-speed hardware counter units to a memory controller. A sending unit periodically samples performance data from the hardware counter units, and transmits count values to a bus interface for an interconnection bus which communicates with the memory controller. The memory controller responsively updates an accumulated count value stored in system memory using the current count value, e.g., incrementing the accumulated count value. A count value can be sent with a pointer to a memory location and an instruction on how the location is to be updated. The instruction may be an atomic read-modify-write operation, and the memory controller can include a dedicated arithmetic logic unit to carry out that operation. A data harvester can then be used to harvest accumulated count values by reading them from a table in system memory.