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2016-01-22ruby: removed Write_Only AccessPermissionBrad Beckmann
2015-07-20ruby: split CPU and GPU latency statsDavid Hashe
2016-01-19gpu-compute: AMD's baseline GPU modelTony Gutierrez
2016-01-19mem: write combining for ruby protocolsTony Gutierrez
This patch adds support for write-combining in ruby.
2016-01-19* * *Tony Gutierrez
mem: support for gpu-style RMWs in ruby This patch adds support for GPU-style read-modify-write (RMW) operations in ruby. Such atomic operations are traditionally executed at the memory controller (instead of through an L1 cache using cache-line locking). Currently, this patch works by propogating operation functors through the memory system.
2015-07-20mem: misc flags for AMD gpu modelBlake Hechtman
This patch add support to mark memory requests/packets with attributes defined in HSA, such as memory order and scope.
2016-01-17sim: fix redundant --debug-start help stringSteve Reinhardt
Just changes the metavar for --debug-start from TIME to TICK in cset 72046b9b3323 and didn't notice that the comment "must be in ticks" is now redundant.
2016-01-17cpu. arch: add initiateMemRead() to ExecContext interfaceSteve Reinhardt
For historical reasons, the ExecContext interface had a single function, readMem(), that did two different things depending on whether the ExecContext supported atomic memory mode (i.e., AtomicSimpleCPU) or timing memory mode (all the other models). In the former case, it actually performed a memory read; in the latter case, it merely initiated a read access, and the read completion did not happen until later when a response packet arrived from the memory system. This led to some confusing things, including timing accesses being required to provide a pointer for the return data even though that pointer was only used in atomic mode. This patch splits this interface, adding a new initiateMemRead() function to the ExecContext interface to replace the timing-mode use of readMem(). For consistency and clarity, the readMemTiming() helper function in the ISA definitions is renamed to initiateMemRead() as well. For x86, where the access size is passed in explicitly, we can also get rid of the data parameter at this level. For other ISAs, where the access size is determined from the type of the data parameter, we have to keep the parameter for that purpose.
2016-01-17cpu: remove unnecessary data ptr from O3 internal read() funcsSteve Reinhardt
The read() function merely initiates a memory read operation; the data doesn't arrive until the access completes and a response packet is received from the memory system. Thus there's no need to provide a data pointer; its existence is historical. Getting this pointer out of this internal o3 interface sets the stage for similar cleanup in the ExecContext interface. Also found that we were pointlessly setting the contents at this pointer on a store forward (the useful memcpy happens just a few lines below the deleted one).
2016-01-17arch: don't call *Timing functions from *Atomic versionsSteve Reinhardt
The readMemAtomic/writeMemAtomic helper functions were calling readMemTiming/writeMemTiming respectively. This is functionally correct, since the *Timing functions are doing the same access initiation operation as the *Atomic functions (just that the *Atomic versions also complete the access in line). It also provides for some (very minimal) code reuse. Unfortunately, it's potentially pretty confusing, since it makes it look like the atomic accesses are somehow being converted to timing accesses. It also gets in the way of specializing the timing interface (as will be done in a future patch).
2016-01-17arch: get rid of unused LargestRead typedefSteve Reinhardt
2016-01-17sim: don't ignore SIG_TRAPSteve Reinhardt
By ignoring SIG_TRAP, using --debug-break <N> when not connected to a debugger becomes a no-op. Apparently this was intended to be a feature, though the rationale is not clear. If we don't ignore SIG_TRAP, then using --debug-break <N> when not connected to a debugger causes the simulation process to terminate at tick N. This is occasionally useful, e.g., if you just want to collect a trace for a specific window of execution then you can combine this with --debug-start to do exactly that. In addition to not ignoring the signal, this patch also updates the --debug-break help message and deletes a handful of unprotected calls to Debug::breakpoint() that relied on the prior behavior.
2016-01-15dev, arm: Add a platform with support for both aarch32 and aarch64Andreas Sandberg
Add a platform with support for both aarch32 and aarch64. This platform implements a subset of the devices in a real Versatile Express and extends it with some gem5-specific functionality. It is in many ways similar to the old VExpress_EMM64 platform, but supports the following new features: * Automatic PCI interrupt assignment * PCI interrupts allocated in a contiguous range. * Automatic boot loader selection (32-bit / 64-bit) * Cleaner memory map where gem5-specific devices live in CS5 which isn't used by current Versatile Express platforms. * No fake devices. Devices that were previously faked will be removed from the device tree instead. * Support for 510 GiB contiguous memory
2016-01-15dev, arm: Add support for automatic PCI interrupt routingAndreas Sandberg
Add support for automatic PCI interrupt routing using a device's ID on the PCI bus. Our current DTBs typically tell the kernel that we do this or something similar when declaring the PCI controller. This changeset adds an option to make the simulator behave in the same way. Interrupt routing can be selected by setting the int_policy parameter in the GenericArmPciHost. The following values are supported: * ARM_PCI_INT_STATIC: Use the old static routing policy using the interrupt line from a device's configurtion space. * ARM_PCI_INT_DEV: Use device number on the PCI bus to map to an interrupt in the GIC. The interrupt is computed as: gic_int = int_base + (pci_dev % int_count) * ARM_PCI_INT_PIN: Use device interrupt pin on the PCI bus to map to an interrupt in the GIC. The PCI specification reserves pin ID 0 for devices without interrupts, the interrupt therefore computed as: gic_int = int_base + ((pin - 1) % int_count)
2016-01-11mem: fix bug in packet access endianness changesSteve Reinhardt
The new Packet::setRaw() method incorrectly still contained an htog() conversion. As a result, calls to the old set() method (now defined as setRaw(htog(v))) underwent two htog conversions, which breaks things when htog() is not a no-op. Interestingly the only test that caught this was a SPARC boot test, where an IsaFake device with a non-zero return value was getting swapped twice resulting in a register getting loaded with 0x100000000000000 instead of 1. (Good reason for keeping SPARC around, perhaps?)
2016-01-11scons: Enable -Wextra by defaultAndreas Hansson
Make best use of the compiler, and enable -Wextra as well as -Wall. There are a few issues that had to be resolved, but they are all trivial.
2016-01-11ext: Replace gzstream with iostream3 from zlib to avoid LGPLAndreas Hansson
This patch replaces the gzstream zlib wrapper with the iostream3 wrapper provided as part of zlib contributions. The main reason for the switch is to avoid including LGPL in the default gem5 build. iostream3 is provided under a more permissive license: The code is provided "as is", with the permission to use, copy, modify, distribute and sell it for any purpose without fee.
2016-01-07dev: Distributed Ethernet link for distributed gem5 simulationsGabor Dozsa
Distributed gem5 (abbreviated dist-gem5) is the result of the convergence effort between multi-gem5 and pd-gem5 (from Univ. of Wisconsin). It relies on the base multi-gem5 infrastructure for packet forwarding, synchronisation and checkpointing but combines those with the elaborated network switch model from pd-gem5. --HG-- rename : src/dev/net/multi_etherlink.cc => src/dev/net/dist_etherlink.cc rename : src/dev/net/multi_etherlink.hh => src/dev/net/dist_etherlink.hh rename : src/dev/net/multi_iface.cc => src/dev/net/dist_iface.cc rename : src/dev/net/multi_iface.hh => src/dev/net/dist_iface.hh rename : src/dev/net/multi_packet.hh => src/dev/net/dist_packet.hh
2016-01-07pseudo inst,util: Add optional key to initparam pseudo instructionGabor Dozsa
The key parameter can be used to read out various config parameters from within the simulated software.
2015-12-31mem: add CacheVerbose debug flag, filter noisy DPRINTFsSteve Reinhardt
Some of the DPRINTFs added to the classic cache in cset 45df88079f04, while useful to those unfamiliar with the cache code, end up being noise when you're familiar with the code but are trying to debug tricky protocol issues. (Particularly getting two messages from each cache as it receives a snoop request then declares that there was no match.) This patch introduces a CacheVerbose debug flag, and moves a subset of the added DPRINTFs into that category, so that Cache by itself returns to being a more succinct summary of cache activity. Also added a CacheAll compound flag to turn on all the cache-related debug flags (other than CacheTags, which you *really* have to want badly to turn it on, IMO).
2015-12-31mem: Do not rely on the NeedsWritable flag for responsesAndreas Hansson
This patch removes the NeedsWritable flag for all responses, as it is really only the request that needs a writable response. The response, on the other hand, should in these cases always provide the line in a writable state, as indicated by the hasSharers flag not being set. When we send requests that has NeedsWritable set, the response will always have the hasSharers flag not set. Additionally, there are cases where the request did not have NeedsWritable set, and we still get a writable response with the hasSharers flag not set. This never happens on snoops, but is used by downstream caches to pass ownership upstream. As part of this patch, the affected response types are updated, and the snoop filter is similarly modified to check only the hasSharers flag (as it should). A sanity check is also added to the packet class, asserting that we never look at the NeedsWritable flag for responses. No regressions are affected.
2015-12-31mem: Do not allocate space for packet data if not neededAndreas Hansson
This patch looks at the request and response command to determine if either actually has any data payload, and if not, we do not allocate any space for packet data. The only tricky case is where the command type is changed as part of the MSHR functionality. In these cases where the original packet had no data, but the new packet does, we need to explicitly call allocate().
2015-12-31mem: Do not alter cache block state on uncacheable snoopsAndreas Hansson
This patch ensures we do not respond with a Modified (dirty and writable) line if the request is uncacheable, and that the cache responding retains the line without modifying the state (even if responding).
2015-12-31mem: Make cache terminology easier to understandAndreas Hansson
This patch changes the name of a bunch of packet flags and MSHR member functions and variables to make the coherency protocol easier to understand. In addition the patch adds and updates lots of descriptions, explicitly spelling out assumptions. The following name changes are made: * the packet memInhibit flag is renamed to cacheResponding * the packet sharedAsserted flag is renamed to hasSharers * the packet NeedsExclusive attribute is renamed to NeedsWritable * the packet isSupplyExclusive is renamed responderHadWritable * the MSHR pendingDirty is renamed to pendingModified The cache states, Modified, Owned, Exclusive, Shared are also called out in the cache and MSHR code to make it easier to understand.
2015-07-20ruby: slicc: have a static MachineTypeTony Gutierrez
This patch is imported from reviewboard patch 2551 by Nilay. This patch moves from a dynamically defined MachineType to a statically defined one. The need for this patch was felt since a dynamically defined type prevents us from having types for which no machine definition may exist. The following changes have been made: i. each machine definition now uses a type from the MachineType enumeration instead of any random identifier. This required changing the grammar and the *.sm files. ii. MachineType enumeration defined statically in RubySlicc_Exports.sm. * * * normal protocol fixes for nilay's parser machine type fix
2015-07-20ruby: slicc: remove support for single machine, multiple typesTony Gutierrez
This patch is imported from reviewboard patch 2550 by Nilay. It was possible to specify multiple machine types with a single state machine. This seems unnecessary and is being removed.
2015-12-28mem: Explicitly check MSHR snoops for cases not dealt withAndreas Hansson
Add a sanity check to make it explicit that we currently do not allow an I/O coherent agent to directly issue writes into the coherent part of the memory system (it has to go via a cache, and get transformed into a read ex, upgrade or invalidation).
2015-12-28mem: Remove unused cache squash functionalityAndreas Hansson
This patch removes the unused squash function from the MSHR queue, and the associated (and also unused) threadNum member from the MSHR.
2015-12-28mem: Avoid unecessary checks when creating HardPFReq in cacheAndreas Hansson
The checks made before sending out a HardPFReq were unecessarily complex, and checked for cases that never occur. This patch tidies it up.
2015-12-28mem: Do not use sender state to track forwarded snoops in cacheAndreas Hansson
This patch changes how the cache tracks which snoops are forwarded, and which ones are created locally. Previously the identification was based on an empty sender state of a specific class, but this method fails to distinguish which cache actually attached the sender state. Instead we use the same mechanism as the crossbar, and keep track of the requests that have outstanding snoops.
2015-12-28mem: Fix cache sender state handling and add clarificationAndreas Hansson
This patch addresses a bug in how the cache attached the MSHR as a sender state. Rather than overwriting any existing sender state it now pushes a new one. The handling of upward snoops is also clarified.
2015-12-18arm: remote GDB: rationalize structure of register offsetsBoris Shingarov
Currently, the wire format of register values in g- and G-packets is modelled using a union of uint8/16/32/64 arrays. The offset positions of each register are expressed as a "register count" scaled according to the width of the register in question. This results in counter- intuitive and error-prone "register count arithmetic", and some formats would even be altogether unrepresentable in such model, e.g. a 64-bit register following a 32-bit one would have a fractional index in the regs64 array. Another difficulty is that the array is allocated before the actual architecture of the workload is known (and therefore before the correct size for the array can be calculated). With this patch I propose a simpler mechanism for expressing the register set structure. In the new code, GdbRegCache is an abstract class; its subclasses contain straightforward structs reflecting the register representation. The determination whether to use e.g. the AArch32 vs. AArch64 register set (or SPARCv8 vs SPARCv9, etc.) is made by polymorphically dispatching getregs() to the concrete subclass. The subclass is not instantiated until it is needed for actual g-/G-packet processing, when the mode is already known. This patch is not meant to be merged in on its own, because it changes the contract between src/base/remote_gdb.* and src/arch/*/remote_gdb.*, so as it stands right now, it would break the other architectures. In this patch only the base and the ARM code are provided for review; once we agree on the structure, I will provide src/arch/*/remote_gdb.* for the other architectures; those patches could then be merged in together. Review Request: http://reviews.gem5.org/r/3207/ Pushed by Joel Hestness <jthestness@gmail.com>
2015-12-18sim: Use the old work item behavior by defaultAndreas Sandberg
When adding an option to forward work items to the Python environment, the new behavior was accidentally enabled by default. Set the value of exit_on_work_items to False by default to revert to the old behavior unless the simulation scripts explicitly requests work item forwarding.
2015-12-17mem: Fix memory allocation bug in deferred snoop handlingAndreas Hansson
This patch fixes a corner case in the deferred snoop handling, where requests ended up being used by multiple packets with different lifetimes, and inadvertently got deleted while they were still in use.
2015-12-14sim: Add an option to forward work items to PythonAndreas Sandberg
There are cases where we want the Python world to handle work items instead of the C++ world. However, that's currently not possible. This changeset adds the forward_work_items option to the System class. Then it is set to True, work items will generate workbegin/workend simulation exists with the work item ID as the exit code and the old C++ handling is completely bypassed. --HG-- extra : rebase_source : 8de637a744fc4b6ff2bc763f00cdf8ddf2bff885
2015-07-20mem: add request types for acquire and releaseDavid Hashe
Add support for acquire and release requests. These synchronization operations are commonly supported by several modern instruction sets.
2015-07-20ruby: more flexible ruby tester supportBrad Beckmann
This patch allows the ruby random tester to use ruby ports that may only support instr or data requests. This patch is similar to a previous changeset (8932:1b2c17565ac8) that was unfortunately broken by subsequent changesets. This current patch implements the support in a more straight-forward way. Since retries are now tested when running the ruby random tester, this patch splits up the retry and drain check behavior so that RubyPort children, such as the GPUCoalescer, can perform those operations correctly without having to duplicate code. Finally, the patch also includes better DPRINTFs for debugging the tester.
2015-12-10dev: Add missing SConscript in src/dev/i2cAndreas Sandberg
2015-12-10dev: Move storage devices to src/dev/storage/Andreas Sandberg
Move the IDE controller and the disk implementations to src/dev/storage. --HG-- rename : src/dev/DiskImage.py => src/dev/storage/DiskImage.py rename : src/dev/Ide.py => src/dev/storage/Ide.py rename : src/dev/SimpleDisk.py => src/dev/storage/SimpleDisk.py rename : src/dev/disk_image.cc => src/dev/storage/disk_image.cc rename : src/dev/disk_image.hh => src/dev/storage/disk_image.hh rename : src/dev/ide_atareg.h => src/dev/storage/ide_atareg.h rename : src/dev/ide_ctrl.cc => src/dev/storage/ide_ctrl.cc rename : src/dev/ide_ctrl.hh => src/dev/storage/ide_ctrl.hh rename : src/dev/ide_disk.cc => src/dev/storage/ide_disk.cc rename : src/dev/ide_disk.hh => src/dev/storage/ide_disk.hh rename : src/dev/ide_wdcreg.h => src/dev/storage/ide_wdcreg.h rename : src/dev/simple_disk.cc => src/dev/storage/simple_disk.cc rename : src/dev/simple_disk.hh => src/dev/storage/simple_disk.hh
2015-12-10dev: Move network devices to src/dev/net/Andreas Sandberg
--HG-- rename : src/dev/Ethernet.py => src/dev/net/Ethernet.py rename : src/dev/etherbus.cc => src/dev/net/etherbus.cc rename : src/dev/etherbus.hh => src/dev/net/etherbus.hh rename : src/dev/etherdevice.cc => src/dev/net/etherdevice.cc rename : src/dev/etherdevice.hh => src/dev/net/etherdevice.hh rename : src/dev/etherdump.cc => src/dev/net/etherdump.cc rename : src/dev/etherdump.hh => src/dev/net/etherdump.hh rename : src/dev/etherint.cc => src/dev/net/etherint.cc rename : src/dev/etherint.hh => src/dev/net/etherint.hh rename : src/dev/etherlink.cc => src/dev/net/etherlink.cc rename : src/dev/etherlink.hh => src/dev/net/etherlink.hh rename : src/dev/etherobject.hh => src/dev/net/etherobject.hh rename : src/dev/etherpkt.cc => src/dev/net/etherpkt.cc rename : src/dev/etherpkt.hh => src/dev/net/etherpkt.hh rename : src/dev/ethertap.cc => src/dev/net/ethertap.cc rename : src/dev/ethertap.hh => src/dev/net/ethertap.hh rename : src/dev/i8254xGBe.cc => src/dev/net/i8254xGBe.cc rename : src/dev/i8254xGBe.hh => src/dev/net/i8254xGBe.hh rename : src/dev/i8254xGBe_defs.hh => src/dev/net/i8254xGBe_defs.hh rename : src/dev/multi_etherlink.cc => src/dev/net/multi_etherlink.cc rename : src/dev/multi_etherlink.hh => src/dev/net/multi_etherlink.hh rename : src/dev/multi_iface.cc => src/dev/net/multi_iface.cc rename : src/dev/multi_iface.hh => src/dev/net/multi_iface.hh rename : src/dev/multi_packet.cc => src/dev/net/multi_packet.cc rename : src/dev/multi_packet.hh => src/dev/net/multi_packet.hh rename : src/dev/ns_gige.cc => src/dev/net/ns_gige.cc rename : src/dev/ns_gige.hh => src/dev/net/ns_gige.hh rename : src/dev/ns_gige_reg.h => src/dev/net/ns_gige_reg.h rename : src/dev/pktfifo.cc => src/dev/net/pktfifo.cc rename : src/dev/pktfifo.hh => src/dev/net/pktfifo.hh rename : src/dev/sinic.cc => src/dev/net/sinic.cc rename : src/dev/sinic.hh => src/dev/net/sinic.hh rename : src/dev/sinicreg.hh => src/dev/net/sinicreg.hh rename : src/dev/tcp_iface.cc => src/dev/net/tcp_iface.cc rename : src/dev/tcp_iface.hh => src/dev/net/tcp_iface.hh
2015-12-10dev: Move i2c functionality to src/dev/i2c/Andreas Sandberg
--HG-- rename : src/dev/I2C.py => src/dev/i2c/I2C.py rename : src/dev/i2cbus.cc => src/dev/i2c/bus.cc rename : src/dev/i2cbus.hh => src/dev/i2c/bus.hh rename : src/dev/i2cdev.hh => src/dev/i2c/device.hh
2015-12-10dev: Move the CopyEngine class to src/dev/pciAndreas Sandberg
--HG-- rename : src/dev/CopyEngine.py => src/dev/pci/CopyEngine.py rename : src/dev/copy_engine.cc => src/dev/pci/copy_engine.cc rename : src/dev/copy_engine.hh => src/dev/pci/copy_engine.hh rename : src/dev/copy_engine_defs.hh => src/dev/pci/copy_engine_defs.hh
2015-12-10dev: Move existing PCI device functionality to src/dev/pciAndreas Sandberg
Move pcidev.(hh|cc) to src/dev/pci/device.(hh|cc) and update existing devices to use the new header location. This also renames the PCIDEV debug flag to have a capitalization that is consistent with the PCI host and other devices. --HG-- rename : src/dev/Pci.py => src/dev/pci/PciDevice.py rename : src/dev/pcidev.cc => src/dev/pci/device.cc rename : src/dev/pcidev.hh => src/dev/pci/device.hh rename : src/dev/pcireg.h => src/dev/pci/pcireg.h
2015-11-05sim: Disable gzip compression for writefile pseudo instructionSascha Bischoff
The writefile pseudo instruction uses OutputDirectory::create and OutputDirectory::openFile to create the output files. However, by default these will check the file extention for .gz, and create a gzip compressed stream if the file ending matches. When writing out files, we want to write them out exactly as they are in the guest simulation, and never want to compress them with gzio. Additionally, this causes m5 writefile to fail when checking the error flags for the output steam. With this patch we add an additional no_gz argument to OutputDirectory::create and OutputDirectory::openFile which allows us to override the gzip compression. Therefore, for m5 writefile we disable the filename check, and always create a standard ostream.
2015-09-18dev, arm: Add gem5 extensions to support more than 8 coresKarthik Sangaiah
Previous ARM-based simulations were limited to 8 cores due to limitations in GICv2 and earlier. This changeset adds a set of gem5-specific extensions that enable support for up to 256 cores. When the gem5 extensions are enabled, the GIC uses CPU IDs instead of a CPU bitmask in the GIC's register interface. To OS can enable the extensions by setting bit 0x200 in ICDICTR. This changeset is based on previous work by Matt Evans.
2015-12-09mem: remove acq/rel cmds from packet and add mem fence reqTony Gutierrez
2015-12-09syscall_emul: don't check host fd when allocating target fdSteve Reinhardt
There's a well-meaning check in Process::allocFD() to return an invalid target fd (-1) if the incoming host fd is -1. However, this means that emulated drivers, which want to allocate a target fd that doesn't correspond to a host fd, can't use -1 to indicate an intentionally invalid host fd. It turns out the allocFD() check is redundant, as callers always test the host fd for validity before calling. Also, callers never test the return value of allocFD() for validity, so even if the test failed, it would likely have the undesirable result of returning -1 to the target app as a file descriptor without setting errno. Thus the check is pointless and is now getting in the way, so it seems we should just get rid of it.
2015-12-07cpu: Support virtual addr in elastic tracesRadhika Jagtap
This patch adds support to optionally capture the virtual address and asid for load/store instructions in the elastic traces. If they are present in the traces, Trace CPU will set those fields of the request during replay.
2015-12-07cpu: Create record type enum for elastic tracesRadhika Jagtap
This patch replaces the booleans that specified the elastic trace record type with an enum type. The source of change is the proto message for elastic trace where the enum is introduced. The struct definitions in the elastic trace probe listener as well as the Trace CPU replace the boleans with the proto message enum. The patch does not impact functionality, but traces are not compatible with previous version. This is preparation for adding new types of records in subsequent patches.
2015-12-07cpu: Add TraceCPU to playback elastic tracesRadhika Jagtap
This patch defines a TraceCPU that replays trace generated using the elastic trace probe attached to the O3 CPU model. The elastic trace is an execution trace with data dependencies and ordering dependencies annoted to it. It also replays fixed timestamp instruction fetch trace that is also generated by the elastic trace probe. The TraceCPU inherits from BaseCPU as a result of which some methods need to be defined. It has two port subclasses inherited from MasterPort for instruction and data ports. It issues the memory requests deducing the timing from the trace and without performing real execution of micro-ops. As soon as the last dependency for an instruction is complete, its computational delay, also provided in the input trace is added. The dependency-free nodes are maintained in a list, called 'ReadyList', ordered by ready time. Instructions which depend on load stall until the responses for read requests are received thus achieving elastic replay. If the dependency is not found when adding a new node, it is assumed complete. Thus, if this node is found to be completely dependency-free its issue time is calculated and it is added to the ready list immediately. This is encapsulated in the subclass ElasticDataGen. If ready nodes are issued in an unconstrained way there can be more nodes outstanding which results in divergence in timing compared to the O3CPU. Therefore, the Trace CPU also models hardware resources. A sub-class to model hardware resources is added which contains the maximum sizes of load buffer, store buffer and ROB. If resources are not available, the node is not issued. The 'depFreeQueue' structure holds nodes that are pending issue. Modeling the ROB size in the Trace CPU as a resource limitation is arguably the most important parameter of all resources. The ROB occupancy is estimated using the newly added field 'robNum'. We need to use ROB number as sequence number is at times much higher due to squashing and trace replay is focused on correct path modeling. A map called 'inFlightNodes' is added to track nodes that are not only in the readyList but also load nodes that are executed (and thus removed from readyList) but are not complete. ReadyList handles what and when to execute next node while the inFlightNodes is used for resource modelling. The oldest ROB number is updated when any node occupies the ROB or when an entry in the ROB is released. The ROB occupancy is equal to the difference in the ROB number of the newly dependency-free node and the oldest ROB number in flight. If no node dependends on a non load/store node then there is no reason to track it in the dependency graph. We filter out such nodes but count them and add a weight field to the subsequent node that we do include in the trace. The weight field is used to model ROB occupancy during replay. The depFreeQueue is chosen to be FIFO so that child nodes which are in program order get pushed into it in that order and thus issued in the in program order, like in the O3CPU. This is also why the dependents is made a sequential container, std::set to std::vector. We only check head of the depFreeQueue as nodes are issued in order and blocking on head models that better than looping the entire queue. An alternative choice would be to inspect top N pending nodes where N is the issue-width. This is left for future as the timing correlation looks good as it is. At the start of an execution event, first we attempt to issue such pending nodes by checking if appropriate resources have become available. If yes, we compute the execute tick with respect to the time then. Then we proceed to complete nodes from the readyList. When a read response is received, sometimes a dependency on it that was supposed to be released when it was issued is still not released. This occurs because the dependent gets added to the graph after the read was sent. So the check is made less strict and the dependency is marked complete on read response instead of insisting that it should have been removed on read sent. There is a check for requests spanning two cache lines as this condition triggers an assert fail in the L1 cache. If it does then truncate the size to access only until the end of that line and ignore the remainder. Strictly-ordered requests are skipped and the dependencies on such requests are handled by simply marking them complete immediately. The simulated seconds can be calculated as the difference between the final_tick stat and the tickOffset stat. A CountedExitEvent that contains a static int belonging to the Trace CPU class as a down counter is used to implement multi Trace CPU simulation exit.