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eb3d5f464d
We're now locking the tail while looking for some room in the ring. In fact it's still while writing to it, but the goal definitely is to get rid of the lock ASAP. For this we reserve the topmost bit of the tail as a lock, which may have as a possible visible effect that buffers will be limited to 2GB instead of 4GB on 32-bit machines (though in practise, good luck for allocating more than 2GB contiguous on 32-bit), but in practice since the size is read with atol() and some operating systems limit it to LONG_MAX unless passing negative numbers, the limit is already there. For now the impact on x86_64 is significant (drop from 2.35 to 1.4M/s on 48 threads on EPYC 24 cores) but this situation is only temporary so that changes can be reviewable and bisectable. Other approaches were attempted, such as using XCHG instead, which is slightly faster on x86 with low thread counts (but causes more write contention), and forces readers to stall under heavy traffic because they can't access a valid value for the queue anymore. A CAS requires preloading the value and is les good on ARMv8.1. XADD could also be considered with 12-13 upper bits of the offset dedicated to locking, but that looks overkill. |
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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)