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By default the GPU VIPER coherence protocol uses a WT L2 cache. However it has support for using WB caches (although this is not tested currently). When using a WB L2 cache for the GPU, this results in deadlocks with loads. Specifically, when a load reaches the L2 and the line is currently in the W state, that line must be written back before the load can be performed. However, the current transition for this in the L2 did not attempt to retry the load when the WB completes, resulting in a deadlock. This deadlock can be replicated by running the GPU Ruby random tester as is with a WB L2 cache instead of a WT L2 cache. To fix this, this change modifies the transition in question to put the load on the stalled requests buffer, which the WBAck will check when it returns to the L2 (and thus perform the load). This fix has been tested and verified with both the per-checkin and nightly GPU Ruby Random tester tests (with a WB L2 cache). Change-Id: Ieec4f61a3070cf9976b8c3ef0cdbd0cc5a1443c6 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/68977 Reviewed-by: Matthew Poremba <matthew.poremba@amd.com> Maintainer: Bobby Bruce <bbruce@ucdavis.edu> 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, 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 these tools. Once you have all dependencies resolved, type 'scons build/<CONFIG>/gem5.opt' where CONFIG is one of the options in build_opts like ARM, NULL, MIPS, POWER, SPARC, X86, Garnet_standalone, etc. This will build an optimized version of the gem5 binary (gem5.opt) with the the specified configuration. See http://www.gem5.org/documentation/general_docs/building for more details and options. The main source tree includes these subdirectories: - build_opts: pre-made default configurations for gem5 - build_tools: tools used internally by gem5's build process. - configs: example simulation configuration scripts - ext: less-common external packages needed to build gem5 - include: include files for use in other programs - site_scons: modular components of the build system - 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 may need compiled system firmware, kernel binaries and one or more disk images, depending on gem5's configuration and what type of workload you're trying to run. Many of those resources can be downloaded from http://resources.gem5.org, and/or from the git repository here: https://gem5.googlesource.com/public/gem5-resources/ If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.