Age | Commit message (Collapse) | Author | |
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2010-10-31 | ISA,CPU,etc: Create an ISA defined PC type that abstracts out ISA behaviors. | Gabe Black | |
This change is a low level and pervasive reorganization of how PCs are managed in M5. Back when Alpha was the only ISA, there were only 2 PCs to worry about, the PC and the NPC, and the lsb of the PC signaled whether or not you were in PAL mode. As other ISAs were added, we had to add an NNPC, micro PC and next micropc, x86 and ARM introduced variable length instruction sets, and ARM started to keep track of mode bits in the PC. Each CPU model handled PCs in its own custom way that needed to be updated individually to handle the new dimensions of variability, or, in the case of ARMs mode-bit-in-the-pc hack, the complexity could be hidden in the ISA at the ISA implementation's expense. Areas like the branch predictor hadn't been updated to handle branch delay slots or micropcs, and it turns out that had introduced a significant (10s of percent) performance bug in SPARC and to a lesser extend MIPS. Rather than perpetuate the problem by reworking O3 again to handle the PC features needed by x86, this change was introduced to rework PC handling in a more modular, transparent, and hopefully efficient way. PC type: Rather than having the superset of all possible elements of PC state declared in each of the CPU models, each ISA defines its own PCState type which has exactly the elements it needs. A cross product of canned PCState classes are defined in the new "generic" ISA directory for ISAs with/without delay slots and microcode. These are either typedef-ed or subclassed by each ISA. To read or write this structure through a *Context, you use the new pcState() accessor which reads or writes depending on whether it has an argument. If you just want the address of the current or next instruction or the current micro PC, you can get those through read-only accessors on either the PCState type or the *Contexts. These are instAddr(), nextInstAddr(), and microPC(). Note the move away from readPC. That name is ambiguous since it's not clear whether or not it should be the actual address to fetch from, or if it should have extra bits in it like the PAL mode bit. Each class is free to define its own functions to get at whatever values it needs however it needs to to be used in ISA specific code. Eventually Alpha's PAL mode bit could be moved out of the PC and into a separate field like ARM. These types can be reset to a particular pc (where npc = pc + sizeof(MachInst), nnpc = npc + sizeof(MachInst), upc = 0, nupc = 1 as appropriate), printed, serialized, and compared. There is a branching() function which encapsulates code in the CPU models that checked if an instruction branched or not. Exactly what that means in the context of branch delay slots which can skip an instruction when not taken is ambiguous, and ideally this function and its uses can be eliminated. PCStates also generally know how to advance themselves in various ways depending on if they point at an instruction, a microop, or the last microop of a macroop. More on that later. Ideally, accessing all the PCs at once when setting them will improve performance of M5 even though more data needs to be moved around. This is because often all the PCs need to be manipulated together, and by getting them all at once you avoid multiple function calls. Also, the PCs of a particular thread will have spatial locality in the cache. Previously they were grouped by element in arrays which spread out accesses. Advancing the PC: The PCs were previously managed entirely by the CPU which had to know about PC semantics, try to figure out which dimension to increment the PC in, what to set NPC/NNPC, etc. These decisions are best left to the ISA in conjunction with the PC type itself. Because most of the information about how to increment the PC (mainly what type of instruction it refers to) is contained in the instruction object, a new advancePC virtual function was added to the StaticInst class. Subclasses provide an implementation that moves around the right element of the PC with a minimal amount of decision making. In ISAs like Alpha, the instructions always simply assign NPC to PC without having to worry about micropcs, nnpcs, etc. The added cost of a virtual function call should be outweighed by not having to figure out as much about what to do with the PCs and mucking around with the extra elements. One drawback of making the StaticInsts advance the PC is that you have to actually have one to advance the PC. This would, superficially, seem to require decoding an instruction before fetch could advance. This is, as far as I can tell, realistic. fetch would advance through memory addresses, not PCs, perhaps predicting new memory addresses using existing ones. More sophisticated decisions about control flow would be made later on, after the instruction was decoded, and handed back to fetch. If branching needs to happen, some amount of decoding needs to happen to see that it's a branch, what the target is, etc. This could get a little more complicated if that gets done by the predecoder, but I'm choosing to ignore that for now. Variable length instructions: To handle variable length instructions in x86 and ARM, the predecoder now takes in the current PC by reference to the getExtMachInst function. It can modify the PC however it needs to (by setting NPC to be the PC + instruction length, for instance). This could be improved since the CPU doesn't know if the PC was modified and always has to write it back. ISA parser: To support the new API, all PC related operand types were removed from the parser and replaced with a PCState type. There are two warts on this implementation. First, as with all the other operand types, the PCState still has to have a valid operand type even though it doesn't use it. Second, using syntax like PCS.npc(target) doesn't work for two reasons, this looks like the syntax for operand type overriding, and the parser can't figure out if you're reading or writing. Instructions that use the PCS operand (which I've consistently called it) need to first read it into a local variable, manipulate it, and then write it back out. Return address stack: The return address stack needed a little extra help because, in the presence of branch delay slots, it has to merge together elements of the return PC and the call PC. To handle that, a buildRetPC utility function was added. There are basically only two versions in all the ISAs, but it didn't seem short enough to put into the generic ISA directory. Also, the branch predictor code in O3 and InOrder were adjusted so that they always store the PC of the actual call instruction in the RAS, not the next PC. If the call instruction is a microop, the next PC refers to the next microop in the same macroop which is probably not desirable. The buildRetPC function advances the PC intelligently to the next macroop (in an ISA specific way) so that that case works. Change in stats: There were no change in stats except in MIPS and SPARC in the O3 model. MIPS runs in about 9% fewer ticks. SPARC runs with 30%-50% fewer ticks, which could likely be improved further by setting call/return instruction flags and taking advantage of the RAS. TODO: Add != operators to the PCState classes, defined trivially to be !(a==b). Smooth out places where PCs are split apart, passed around, and put back together later. I think this might happen in SPARC's fault code. Add ISA specific constructors that allow setting PC elements without calling a bunch of accessors. Try to eliminate the need for the branching() function. Factor out Alpha's PAL mode pc bit into a separate flag field, and eliminate places where it's blindly masked out or tested in the PC. | |||
2010-08-23 | ARM: mark msr/mrs instructions as SerializeBefore/After | Min Kyu Jeong | |
Since miscellaneous registers bypass wakeup logic, force serialization to resolve data dependencies through them * * * ARM: adding non-speculative/serialize flags for instructions change CPSR | |||
2010-08-23 | ARM/O3: store the result of the predicate evaluation in DynInst or Threadstate. | Min Kyu Jeong | |
THis allows the CPU to handle predicated-false instructions accordingly. This particular patch makes loads that are predicated-false to be sent straight to the commit stage directly, not waiting for return of the data that was never requested since it was predicated-false. | |||
2009-09-23 | arch: nuke arch/isa_specific.hh and move stuff to generated config/the_isa.hh | Nathan Binkert | |
2008-11-10 | O3CPU: Make the instcount debugging stuff per-cpu. | Clint Smullen | |
This is to prevent the assertion from firing if you have a large multicore. Also make sure that it's not compiled in when NDEBUG is defined | |||
2008-03-06 | O3CPU: Don't call dumpInsts if DEBUG is not defined | Vilas Sridharan | |
--HG-- extra : convert_revision : 3194bde4c624d118969bfbf92282539963a72245 | |||
2007-06-20 | Fix compiler errors. | Gabe Black | |
--HG-- extra : convert_revision : 2b10076a24cb36cb748e299011ae691f09c158cd | |||
2007-04-14 | Add support for microcode and pull out the special branch delay slot ↵ | Gabe Black | |
handling. Branch delay slots need to be squash on a mispredict as well because the nnpc they saw was incorrect. --HG-- extra : convert_revision : 8b9c603616bcad254417a7a3fa3edfb4c8728719 | |||
2007-03-23 | Two fixes: | Kevin Lim | |
1. Requests are handled more properly now. They assume the memory system takes control of the request upon sending out an access. 2. load-load ordering is maintained. src/cpu/base_dyn_inst.hh: Update how requests are handled. The BaseDynInst should not be able to hold a pointer to the request because the request becomes owned by the memory system once it is sent out. Also include some functions to allow certain status bits to be cleared. src/cpu/base_dyn_inst_impl.hh: Update how requests are handled. The BaseDynInst should not be able to hold a pointer to the request because the request becomes owned by the memory system once it is sent out. src/cpu/o3/fetch_impl.hh: General correctness fixes. retryPkt is not necessarily always set, so handle it properly. Also consider the cache unblocked only when recvRetry is called. src/cpu/o3/lsq_unit.hh: Handle requests a little more correctly. Now that the requests aren't pointed to by the DynInst, be sure to delete the request if it's not being used by the memory system. Also be sure to not store-load forward from an uncacheable store. src/cpu/o3/lsq_unit_impl.hh: Check to make sure load-load ordering was maintained. Also handle requests a little more correctly. --HG-- extra : convert_revision : e86bead2886d02443cf77bf7a7a1492845e1690f | |||
2006-12-16 | Accidently "cleaned" away the NPC parameter to the constructor. | Gabe Black | |
--HG-- extra : convert_revision : 46670ee86000dfb171d327eb8f58555a4afb2360 | |||
2006-12-16 | Added a predicted NPC field, explicitly stored whether the instruction was ↵ | Gabe Black | |
predicted taken or not. --HG-- extra : convert_revision : ba668af302ca4d8a3a032e907d5058e1477f462a | |||
2006-10-23 | Add in support for LL/SC in the O3 CPU. Needs to be fully tested. | Kevin Lim | |
src/cpu/base_dyn_inst.hh: Extend BaseDynInst a little bit so it can be use as a TC as well (specifically for ll/sc code). src/cpu/base_dyn_inst_impl.hh: Add variable to track if the result of the instruction should be recorded. src/cpu/o3/alpha/cpu_impl.hh: Clear lock flag upon hwrei. src/cpu/o3/lsq_unit.hh: Use ISA specified handling of locked reads. src/cpu/o3/lsq_unit_impl.hh: Use ISA specified handling of locked writes. --HG-- extra : convert_revision : 1f5c789c35deb4b016573c02af4aab60d726c0e5 | |||
2006-10-08 | Replace tests of LOCKED/UNCACHEABLE flags with isLocked()/isUncacheable(). | Steve Reinhardt | |
--HG-- extra : convert_revision : f22ce3221d270ecf8631d3dcaed05753accd5461 | |||
2006-08-15 | Cleaned up include files and got rid of many using directives in header files. | Gabe Black | |
--HG-- extra : convert_revision : 6b11e039cbc061dab75195fa1aebe6ca2cdc6f91 | |||
2006-07-23 | This changeset gets the MIPS ISA pretty much working in the O3CPU. It ↵ | Korey Sewell | |
builds, runs, and gets very very close to completing the hello world succesfully but there are some minor quirks to iron out. Who would've known a DELAY SLOT introduces that much complexity?! arrgh! Anyways, a lot of this stuff had to do with my project at MIPS and me needing to know how I was going to get this working for the MIPS ISA. So I figured I would try to touch it up and throw it in here (I hate to introduce non-completely working components... ) src/arch/alpha/isa/mem.isa: spacing src/arch/mips/faults.cc: src/arch/mips/faults.hh: Gabe really authored this src/arch/mips/isa/decoder.isa: add StoreConditional Flag to instruction src/arch/mips/isa/formats/basic.isa: Steven really did this file src/arch/mips/isa/formats/branch.isa: fix bug for uncond/cond control src/arch/mips/isa/formats/mem.isa: Adjust O3CPU memory access to use new memory model interface. src/arch/mips/isa/formats/util.isa: update LoadStoreBase template src/arch/mips/isa_traits.cc: update SERIALIZE partially src/arch/mips/process.cc: src/arch/mips/process.hh: no need for this for NOW. ASID/Virtual addressing handles it src/arch/mips/regfile/misc_regfile.hh: add in clear() function and comments for future usage of special misc. regs src/cpu/base_dyn_inst.hh: add in nextNPC variable and supporting functions. add isCondDelaySlot function Update predTaken and mispredicted functions src/cpu/base_dyn_inst_impl.hh: init nextNPC src/cpu/o3/SConscript: add MIPS files to compile src/cpu/o3/alpha/thread_context.hh: no need for my name on this file src/cpu/o3/bpred_unit_impl.hh: Update RAS appropriately for MIPS src/cpu/o3/comm.hh: add some extra communication variables to aid in handling the delay slots src/cpu/o3/commit.hh: minor name fix for nextNPC functions. src/cpu/o3/commit_impl.hh: src/cpu/o3/decode_impl.hh: src/cpu/o3/fetch_impl.hh: src/cpu/o3/iew_impl.hh: src/cpu/o3/inst_queue_impl.hh: src/cpu/o3/rename_impl.hh: Fix necessary variables and functions for squashes with delay slots src/cpu/o3/cpu.cc: Update function interface ... adjust removeInstsNotInROB function to recognize delay slots insts src/cpu/o3/cpu.hh: update removeInstsNotInROB src/cpu/o3/decode.hh: declare necessary variables for handling delay slot src/cpu/o3/dyn_inst.hh: Add in MipsDynInst src/cpu/o3/fetch.hh: src/cpu/o3/iew.hh: src/cpu/o3/rename.hh: declare necessary variables and adjust functions for handling delay slot src/cpu/o3/inst_queue.hh: src/cpu/simple/base.cc: no need for my name here src/cpu/o3/isa_specific.hh: add in MIPS files src/cpu/o3/scoreboard.hh: dont include alpha specific isa traits! src/cpu/o3/thread_context.hh: no need for my name here, i just rearranged where the file goes src/cpu/static_inst.hh: add isCondDelaySlot function src/cpu/o3/mips/cpu.cc: src/cpu/o3/mips/cpu.hh: src/cpu/o3/mips/cpu_builder.cc: src/cpu/o3/mips/cpu_impl.hh: src/cpu/o3/mips/dyn_inst.cc: src/cpu/o3/mips/dyn_inst.hh: src/cpu/o3/mips/dyn_inst_impl.hh: src/cpu/o3/mips/impl.hh: src/cpu/o3/mips/params.hh: src/cpu/o3/mips/thread_context.cc: src/cpu/o3/mips/thread_context.hh: MIPS file for O3CPU...mirrors ALPHA definition --HG-- extra : convert_revision : 9bb199b4085903e49ffd5a4c8ac44d11460d988c | |||
2006-06-17 | Split off instantiation into separate CC files for each of the models. This ↵ | Kevin Lim | |
makes it easier to be able to specify only certain CPU models. src/cpu/SConscript: Split off instantiations into separate CC files. This makes it easier to split them per CPU model. src/cpu/base_dyn_inst_impl.hh: Move instantations out of impl.hh file and into a cc file. src/cpu/checker/cpu_impl.hh: Move instantiations over to .cc files inside each CPU's directory. Makes it easier to only use what's actually included. src/cpu/o3/bpred_unit.cc: Pull Ozone instantiations out of this .cc file; put them into the ozone's CC file. src/cpu/o3/checker_builder.cc: Instantiate Checker for O3 CPU. src/cpu/ozone/checker_builder.cc: Instantiate Checker for Ozone CPU. --HG-- rename : src/cpu/base_dyn_inst.cc => src/cpu/base_dyn_inst_impl.hh rename : src/cpu/checker/cpu.cc => src/cpu/checker/cpu_impl.hh rename : src/cpu/checker/o3_builder.cc => src/cpu/o3/checker_builder.cc rename : src/cpu/checker/ozone_builder.cc => src/cpu/ozone/checker_builder.cc extra : convert_revision : 4e5f928b165379c06d31071c544ea46cf0b8fa71 |