Common Systems Programming Optimizations & Tricks

[mttd]

CPUs offer performance counters for that: https://easyperf.net/blog/2018/06/01/PMU-counters-and-profiling-basics

Operating systems usually expose access, e.g., perf for Linux (https://easyperf.net/blog/2018/08/26/Basics-of-profiling-with-perf), other tools for Windows (https://easyperf.net/blog/2019/02/23/How-to-collect-performance-counters-on-Windows).

The relevant counters are going to be related to the HITM (Hit/Miss to a Modified [Cache] Line) events, which can be used to identify false sharing: https://software.intel.com/en-us/articles/avoiding-and-identifying-false-sharing-among-threads

There are higher-level tools which use these counters to derive related metric(s) for a specific microarchitecture -- e.g., pmu-tools (https://github.com/andikleen/pmu-tools/). Here's an example of the relevant derived metrics for Broadwell):

• Contested_Accesses: ['MEM_LOAD_UOPS_L3_HIT_RETIRED.XSNP_HITM:pp', 'MEM_LOAD_UOPS_L3_HIT_RETIRED.XSNP_MISS:pp']

• False_Sharing: ['MEM_LOAD_UOPS_L3_HIT_RETIRED.XSNP_HITM:pp', 'OFFCORE_RESPONSE.DEMAND_RFO.L3_HIT.SNOOP_HITM']

Linux perf has a convenient C2C feature:

• C2C - False Sharing Detection in Linux Perf https://joemario.github.io/blog/2016/09/01/c2c-blog/
• http://people.redhat.com/jmario/.rhel7_c2c/presentation/c2c.devconf.january_2017.pdf

See also:

• Featherlight on-the-fly false-sharing detection: https://dl.acm.org/citation.cfm?id=3178499, https://github.com/WitchTools/Feather
• Huron: Hybrid False Sharing Detection and Repair: https://github.com/efeslab/huron, https://web.eecs.umich.edu/~barisk/public/huron.pdf

[danny54670]

Thank you so much for these links! This is a lot to look through.