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If a set of LL/SC requests contend on the same cache block we can get into a situation where CPUs will deadlock if they expect a failed SC to supply them data. This case happens where 3 or more cores are contending for a cache block using LL/SC and the system is configured where 2 cores are connected to a local bus and the third is connected to a remote bus. If a core on the local bus sends an SCUpgrade and the core on the remote bus sends and SCUpgrade they will race to see who will win the SC access. In the meantime if the other core appends a read to one of the SCUpgrades it will expect to be supplied data by that SCUpgrade transaction. If it happens that the SCUpgrade that was picked to supply the data is failed, it will drop the appended request for data and never respond, leaving the requesting core to deadlock. This patch makes all SC's behave as normal stores to prevent this case but still makes sure to check whether it can perform the update.
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/Introduction, and for more information about building the simulator and getting started please see http://www.gem5.org/Documentation and http://www.gem5.org/Tutorials. 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/Dependencies 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 ALPHA, 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/Build_System for more details and options. With the simulator built, have a look at http://www.gem5.org/Running_gem5 for more information on how to use gem5. 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. Please see the gem5 download page for these items at http://www.gem5.org/Download If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.