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Barriers were not modeled properly. Firstly, barriers were allocated to each WG that was launched, which is not correct, and the CU would provide an infinite number of barrier slots. There are a limited number of barrier slots per CU in reality. In addition, the CU will not allocate barrier slots to WGs with a single WF (nothing to sync if only one WF). Beyond modeling problems, there also the issue of deadlock. The barrier could deadlock because not all WFs are freed from the barrier once it has been satisfied. Instead, we relied on the scoreboard stage to release them lazily, one-by-one. Under this implementation the scoreboard may not fully release all WFs participating in a barrier; this happens because the first WF to be freed from the barrier could reach an s_barrier instruction again, forever causing the barrier counts across WFs to be out-of-sync. This change refactors the barrier logic to: 1) Create a proper barrier slot implementation 2) Enforce (via a parameter) the number of barrier slots on the CU. 3) Simplify the logic and cleanup the code (i.e., we no longer iterate through the entire WF list each time we check if a barrier is satisfied). 4) Fix deadlock issues. Change-Id: If53955b54931886baaae322640a7b9da7a1595e0 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/29943 Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com> Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com> Tested-by: kokoro <noreply+kokoro@google.com>
This is the gem5 simulator. The main website can be found at http://www.gem5.org A good starting point is http://www.gem5.org/about, and for more information about building the simulator and getting started please see http://www.gem5.org/documentation and http://www.gem5.org/documentation/learning_gem5/introduction. To build gem5, you will need the following software: g++ or clang, Python (gem5 links in the Python interpreter), SCons, SWIG, zlib, m4, and lastly protobuf if you want trace capture and playback support. Please see http://www.gem5.org/documentation/general_docs/building for more details concerning the minimum versions of the aforementioned tools. Once you have all dependencies resolved, type 'scons build/<ARCH>/gem5.opt' where ARCH is one of ARM, NULL, MIPS, POWER, SPARC, or X86. This will build an optimized version of the gem5 binary (gem5.opt) for the the specified architecture. See http://www.gem5.org/documentation/general_docs/building for more details and options. The basic source release includes these subdirectories: - configs: example simulation configuration scripts - ext: less-common external packages needed to build gem5 - src: source code of the gem5 simulator - system: source for some optional system software for simulated systems - tests: regression tests - util: useful utility programs and files To run full-system simulations, you will need compiled system firmware (console and PALcode for Alpha), kernel binaries and one or more disk images. If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.