Arsalan Shahid

Performance Monitoring Counters and Process Monitoring Tools in Linux

My dear reader, how are you? السلام عليكم

Perseverance is stubbornness with a purpose – Josh Shipp

In this post, I explain the standard tools to collect performance monitoring tools in modern computing platforms. Furthermore,  we explore the standard tools to collect utilization metrics for the execution of applications in Linux.

Performance Monitoring Counters (PMCs)

Performance events or performance monitoring counters (PMCs) are special-purpose registers provided in modern microprocessors to store the counts of software and hardware activities. They include software events, which are pure kernel-level counters such as page faults, context switches, etc. as well as micro-architectural events originating from the processor and its performance monitoring unit called the hardware events such as cache misses, branch instructions, etc. PMCs have been developed primarily to aid low-level performance analysis and tuning.

Significant Properties

The following are some of the significant properties of PMCs.

  1. PMCs are typically large in number. For example, a typical Intel Haswell  CPU has 164 PMCs whereas Intel Skylake processors have 385 PMCs.
  2. They can not be collected all together because of a limited number of registers dedicated to storing them. 3 or 4 PMCs can be collected in one application run.
  3. So, the collection of all PMCs for application execution on a platform is a
    tedious task.
  4. PMCs are architecture-specific. PMCs on an Intel processor may not be available for an ARM processor or a GPU.

Tools to obtain PMCs

Collection of PMCs on Modern Intel-based Server Using Likwid Tool

Using Likwid tool, we now explain the collection of PMCs on an Intel Haswell multicore and dual-socket CPU with specifications given as below:

Hardware topology can be viewed using likwid-topology tool.

PMCs can be collected using likwid-perfctr tool. The following commands are useful to understand what PMCs and metrics can be accessed using Likwid on a given platform.

A sample Likwid command-line invocation is shown below where EVENTS
represents one or more PMCs, which are collected during the execution of the given application APP:

$ likwid-perfctr -f -C S0:0-11,24-35@S1:12-23,36-47 -g EVENTS ./APP

Here, the application (APP) during its execution is pinned to physical cores ( 0-24) in our platform.
For example, the following command:

$ likwid-perfctr -f -C S0:0-11,24-35@S1:12-23,36-47 -g ICACHE_ACCESSES:PMC0,ICACHE_MISSES:PMC1 ./APP

The above command determines the counts for two PMCs, ICACHE_ACCESSES :PMC0 and ICACHE_MISSES :PMC1. Likwid uses likwid-pin for core pinning.

Resource Pinning

Since Likwid do not provide the option to bind the application to memory
– We can use numactl, i.e., a command-line Linux tool, with option membind to pin our applications to memory blocks
– For our platform numactl gives 2 memory blocks, 0 and 1. The list of comma-separated PMCs is specified in EVENTS.

$ likwid-perfctr -f -C S0:0-11,24-35@S1:12-23,36-47 -g ICACHE_ACCESSES:PMC0,ICACHE_MISSES:PMC1 numactl --membind =0,1 ./APP

Numactl can also be used to pin the applications to cores as shown below:

$ numactl --physcpubind=0-47 ./APP

Linux tools to monitor processes and threads

The following are some of the useful Linux tools to monitor the process during its execution on a processor.

I hope you find this post useful. If you find any errors or feel any need for improvement, let me know in your comments below.

Signing off for today. Stay tuned and I will see you in my next post! Happy learning.

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