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If the memory system can provide a back door to memory, store that, and use it for subsequent accesses to the range it covers. For now, this covers only fetch. That's because fetch will generally happen more than loads and stores, and because it's relatively simple to implement since we can ignore atomic operations, etc. Some limitted benchmarking suggests that this speeds up x86 linux boot by about 20%, although my modifications to the config to remove caching (which blocks the back door mechanism) also made gem5 crash, so it's hard to say for sure if that's a valid result. The crash happened in the same way before and after, so it's probably at least relatively representative. While this gives a pretty substantial performance boost, it will prevent statistics from being collected at the memory, or on intermediate objects in the interconnect like the bus. That is to be expected with this memory mode, however. Change-Id: I73f73017e454300fd4d61f58462eb4ec719b8d85 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36979 Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Jason Lowe-Power <power.jg@gmail.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.