At the same time, rename the trace flags to debug flags since they
have broader usage than simply tracing. This means that
--trace-flags is now --debug-flags and --trace-help is now --debug-help
Some ISAs (like ARM) relies on hardware page table walkers. For those ISAs,
when a TLB miss occurs, initiateTranslation() can return with NoFault but with
the translation unfinished.
Instructions experiencing a delayed translation due to a hardware page table
walk are deferred until the translation completes and kept into the IQ. In
order to keep track of them, the IQ has been augmented with a queue of the
outstanding delayed memory instructions. When their translation completes,
instructions are re-executed (only their initiateAccess() was already
executed; their DTB translation is now skipped). The IEW stage has been
modified to support such a 2-pass execution.
This change modifies the way prefetches work. They are now like normal loads
that don't writeback a register. Previously prefetches were supposed to call
prefetch() on the exection context, so they executed with execute() methods
instead of initiateAcc() completeAcc(). The prefetch() methods for all the CPUs
are blank, meaning that they get executed, but don't actually do anything.
On Alpha dead cache copy code was removed and prefetches are now normal ops.
They count as executed operations, but still don't do anything and IsMemRef is
not longer set on them.
On ARM IsDataPrefetch or IsInstructionPreftech is now set on all prefetch
instructions. The timing simple CPU doesn't try to do anything special for
prefetches now and they execute with the normal memory code path.
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.
Since miscellaneous registers bypass wakeup logic, force serialization
to resolve data dependencies through them
* * *
ARM: adding non-speculative/serialize flags for instructions change CPSR
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.
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
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
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
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
