Count read and write accesses to memory

Question

On a Linux machine, I need to count the number of read and write accesses to memory (DRAM) performed by a process. The machine has a NUMA configuration and I am binding the process to access memory from a single remote NUMA node using numactl. The process is running on CPUs in node 0 and accessing memory in node 1.

Currently, I am using perf to count the number of LLC load miss and LLC store miss events to serve as an estimate for read and write accesses to memory. Because, I guessed LLC misses will need to be served by memory accesses. Is this approach correct i.e. is this event relevant ? And, are there any alternatives to obtain the read and write access information ?

Processor : Intel Xeon E5-4620 Kernel : Linux 3.9.0+

Answer 1

Depending on your hardware you should be able to acess performance counter located on the memory side, to exactly count memory accesses. On Intel processor, these events are called uncore events. I know that you can also count the same thing on AMD processors.

Counting LLC misses is not totally correct because some events such as the hardware prefetcher may lead a significant number of memory accesses.

Regarding your hardware, unfortunately you will have to use raw events (in the perf terminology). These events can't be generalized by perf because they are processor's specifics and as a consequence you will have to look into your processor's manual to find the raw encoding of the event to give to perf. For your Intel processor you should look at chapter 18.9.8 Intel® Xeon® Processor E5 Family Uncore Performance Monitoring Facility and CHAPTER 19 PERFORMANCE-MONITORING EVENTS of the Intel software developer manual document available here In these documents you'll need the exact ID of your processor that you can get using /proc/cpuinfo