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On highly threaded machines it is possible to occasionally trigger the watchdog on certain contended areas like the server's connection list, because while the mechanism inherently cannot guarantee a constant progress, it lacks CPU relax calls which are absolutely necessary in this situation to let a thread finish its job. The loop's "while (1)" was changed to use a "for" statement calling __ha_cpu_relax() as its continuation expression. This way the "continue" statements jump to the unique place containing the pause without excessively inflating the code. This was sufficient to definitely fix the problem on 64-core ARM Graviton2 machines. This patch should probably be backported once it's confirmed it also helps on many-cores x86 machines since some people are facing contention in these environments. This patch depends on previous commit "REORG: atomic: reimplement pl_cpu_relax() from atomic-ops.h". An attempt was made to first read the value before exchanging, and it significantly degraded the performance. It's very likely that this caused other cores to lose exclusive ownership on their line and slow down their next xchg operation. In addition it was found that MT_LIST_ADD is significantly faster than MT_LIST_ADDQ under high contention, because it fails one step earlier when conflicting with an adjacent MT_LIST_DEL(). It might be worth switching some operations' order to favor MT_LIST_ADDQ() instead.
The HAProxy documentation has been split into a number of different files for ease of use. Please refer to the following files depending on what you're looking for : - INSTALL for instructions on how to build and install HAProxy - BRANCHES to understand the project's life cycle and what version to use - LICENSE for the project's license - CONTRIBUTING for the process to follow to submit contributions The more detailed documentation is located into the doc/ directory : - doc/intro.txt for a quick introduction on HAProxy - doc/configuration.txt for the configuration's reference manual - doc/lua.txt for the Lua's reference manual - doc/SPOE.txt for how to use the SPOE engine - doc/network-namespaces.txt for how to use network namespaces under Linux - doc/management.txt for the management guide - doc/regression-testing.txt for how to use the regression testing suite - doc/peers.txt for the peers protocol reference - doc/coding-style.txt for how to adopt HAProxy's coding style - doc/internals for developer-specific documentation (not all up to date)