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This patch does a large modification of the LSQ in the O3 model. The main goal of the patch is to remove the 'an operation can be served with one or two memory requests' assumption that is present in the LSQ and the instruction with the req, reqLow, reqHigh triplet, and generalising it to operations that can be addressed with one request, and operations that require many requests, embodied in the SingleDataRequest and the SplitDataRequest. This modification has been done mimicking the minor model to an extent, shifting the responsibilities of dealing with VtoP translation and tracking the status and resources from the DynInst to the LSQ via the LSQRequest. The LSQRequest models the information concerning the operation, handles the creation of fragments for translation and request as well as assembling/splitting the data accordingly. With this modifications, the implementation of vector ISAs, particularly on the memory side, become more rich, as the new model permits a dissociation of the ISA characteristics as vector length, from the microarchitectural characteristics that govern how contiguous loads are executing, allowing exploration of different LSQ to DL1 bus widths to understand the tradeoffs in complexity and performance. Part of the complexities introduced stem from the fact that gem5 keeps a large amount of metadata regarding, in particular, memory operations, thus, when an instruction is squashed while some operation as TLB lookup or cache access is ongoing, when the relevant structure communicates to the LSQ that the operation is over, it tries to access some pieces of data that should have died when the instruction is squashed, leading to asserts, panics, or memory corruption. To ensure the correct behaviour, the LSQRequest rely on assesing who is their owner, and self-destroying if they detect their owner is done with the request, and there will be no subsequent action. For example, in the case of an instruction squashed whal the TLB is doing a walk to serve the translation, when the translation is served by the TLB, the LSQRequest detects that the instruction was squashed, and as the translation is done, no one else expect to access its information, and therefore, it self-destructs. Having destroyed the LSQRequest earlier, would lead to wrong behaviour as the TLB walk may access some fields of it. Additional authors: - Gabor Dozsa <gabor.dozsa@arm.com> Change-Id: I9578a1a3f6b899c390cdd886856a24db68ff7d0c Signed-off-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com> Reviewed-on: https://gem5-review.googlesource.com/c/13516 Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com> Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.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/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.