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2017-03-17syscall-emul: Hotfix for FreeBSD/Mac buildsBrandon Potter
The clone system call added in 236719892 relies on header files from Linux systems. Obviously, this prevents compilation for anyone using FreeBSD or Mac to compile the simulator. This changeset is meant as a temporary fix to allow builds on non-Linux systems until a proper solution is found. Change-Id: I404cc41c588ed193dd2c1ca0c1aea35b0786fe4e Reviewed-on: https://gem5-review.googlesource.com/2420 Maintainer: Brandon Potter <Brandon.Potter@amd.com> Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
2017-03-17syscall-emul: change NULL to nullptr in Process filesBrandon Potter
Change-Id: I9ff21092876593237f919e9f7fb7283bd865ba2e Reviewed-on: https://gem5-review.googlesource.com/2421 Reviewed-by: Jason Lowe-Power <jason@lowepower.com> Maintainer: Brandon Potter <Brandon.Potter@amd.com>
2017-03-09syscall-emul: Rewrite system call exit codeBrandon Potter
The changeset does a major refactor on the exit, exit_group, and futex system calls regarding exit functionality. A FutexMap class and related structures are added into a new file. This increases code clarity by encapsulating the futex operations and the futex state into an object. Several exit conditions were added to allow the simulator to end processes under certain conditions. Also, the simulation only exits now when all processes have finished executing. Change-Id: I1ee244caa9b5586fe7375e5b9b50fd3959b9655e Reviewed-on: https://gem5-review.googlesource.com/2269 Maintainer: Jason Lowe-Power <jason@lowepower.com> Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
2017-03-09style: Correct some style issuesBrandon Potter
This changeset fixes line alignment issues, spacing, spelling, etc. for files that are used during SE Mode. Change-Id: Ie61b8d0eb4ebb5af554d72f1297808027833616e Reviewed-on: https://gem5-review.googlesource.com/2264 Maintainer: Jason Lowe-Power <jason@lowepower.com> Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com> Reviewed-by: Michael LeBeane <Michael.Lebeane@amd.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Pierre-Yves Péneau <pierre-yves.peneau@lirmm.fr>
2017-03-09syscall-emul: Move memState into its own fileBrandon Potter
The Process class is full of implementation details and structures related to SE Mode. This changeset factors out an internal class from Process and moves it into a separate file. The purpose behind doing this is to clean up the code and make it a bit more modular. Change-Id: Ic6941a1657751e8d51d5b6b1dcc04f1195884280 Reviewed-on: https://gem5-review.googlesource.com/2263 Reviewed-by: Jason Lowe-Power <jason@lowepower.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2017-02-27syscall_emul: [PATCH 15/22] add clone/execve for threading and multiprocess ↵Brandon Potter
simulations Modifies the clone system call and adds execve system call. Requires allowing processes to steal thread contexts from other processes in the same system object and the ability to detach pieces of process state (such as MemState) to allow dynamic sharing.
2017-02-27syscall_emul: [patch 14/22] adds identifier system callsBrandon Potter
This changeset add fields to the process object and adds the following three system calls: setpgid, gettid, getpid.
2015-07-20syscall_emul: [patch 13/22] add system call retry capabilityBrandon Potter
This changeset adds functionality that allows system calls to retry without affecting thread context state such as the program counter or register values for the associated thread context (when system calls return with a retry fault). This functionality is needed to solve problems with blocking system calls in multi-process or multi-threaded simulations where information is passed between processes/threads. Blocking system calls can cause deadlock because the simulator itself is single threaded. There is only a single thread servicing the event queue which can cause deadlock if the thread hits a blocking system call instruction. To illustrate the problem, consider two processes using the producer/consumer sharing model. The processes can use file descriptors and the read and write calls to pass information to one another. If the consumer calls the blocking read system call before the producer has produced anything, the call will block the event queue (while executing the system call instruction) and deadlock the simulation. The solution implemented in this changeset is to recognize that the system calls will block and then generate a special retry fault. The fault will be sent back up through the function call chain until it is exposed to the cpu model's pipeline where the fault becomes visible. The fault will trigger the cpu model to replay the instruction at a future tick where the call has a chance to succeed without actually going into a blocking state. In subsequent patches, we recognize that a syscall will block by calling a non-blocking poll (from inside the system call implementation) and checking for events. When events show up during the poll, it signifies that the call would not have blocked and the syscall is allowed to proceed (calling an underlying host system call if necessary). If no events are returned from the poll, we generate the fault and try the instruction for the thread context at a distant tick. Note that retrying every tick is not efficient. As an aside, the simulator has some multi-threading support for the event queue, but it is not used by default and needs work. Even if the event queue was completely multi-threaded, meaning that there is a hardware thread on the host servicing a single simulator thread contexts with a 1:1 mapping between them, it's still possible to run into deadlock due to the event queue barriers on quantum boundaries. The solution of replaying at a later tick is the simplest solution and solves the problem generally.
2016-11-09syscall_emul: [patch 10/22] refactor fdentry and add fdarray classBrandon Potter
Several large changes happen in this patch. The FDEntry class is rewritten so that file descriptors now correspond to types: 'File' which is normal file-backed file with the file open on the host machine, 'Pipe' which is a pipe that has been opened on the host machine, and 'Device' which does not have an open file on the host yet acts as a pseudo device with which to issue ioctls. Other types which might be added in the future are directory entries and sockets (off the top of my head). The FDArray class was create to hold most of the file descriptor handling that was stuffed into the Process class. It uses shared pointers and the std::array type to hold the FDEntries mentioned above. The changes to these two classes needed to be propagated out to the rest of the code so there were quite a few changes for that. Also, comments were added where I thought they were needed to help others and extend our DOxygen coverage.
2016-11-09syscall_emul: [patch 9/22] remove unused global variable (num_processes)Brandon Potter
2016-11-09syscall_emul: [patch 8/22] refactor process classBrandon Potter
Moves aux_vector into its own .hh and .cc files just to get it out of the already crowded Process files. Arguably, it could stay there, but it's probably better just to move it and give it files. The changeset looks ugly around the Process header file, but the goal here is to move methods and members around so that they're not defined randomly throughout the entire header file. I expect this is likely one of the reasons why I several unused variables related to this class. So, the methods are declared first followed by members. I've tried to aggregate them together so that similar entries reside near one another. There are other changes coming to this code so this is by no means the final product.
2016-11-09syscall_emul: [patch 6/22] remove unused fields from Process classBrandon Potter
It looks like tru64 has some nxm* system calls, but the two fields that are defined in the Process class are unused by any of the code. There doesn't appear to be any reference in the tru64 code.
2016-11-09syscall_emul: [patch 5/22] remove LiveProcess class and use Process insteadBrandon Potter
The EIOProcess class was removed recently and it was the only other class which derived from Process. Since every Process invocation is also a LiveProcess invocation, it makes sense to simplify the organization by combining the fields from LiveProcess into Process.
2017-02-09sim: fix build breakage in process.cc after brandon@11801Bjoern A. Zeeb
Seeing build breakage after brandon@11801: [ CXX] X86/sim/process.cc -> .o build/X86/sim/process.cc:137:64: error: field '_pid' is uninitialized when used here [-Werror,-Wuninitialized] static_cast<PageTableBase *>(new ArchPageTable(name(), _pid, system)) : ^ build/X86/sim/process.cc:138:64: error: field '_pid' is uninitialized when used here [-Werror,-Wuninitialized] static_cast<PageTableBase *>(new FuncPageTable(name(), _pid))), ^ 2 errors generated. Testing Done: Compiles now on FreeBSD 10 with clang. Reviewed at http://reviews.gem5.org/r/3804/ Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
2016-11-09syscall_emul: [patch 4/22] remove redundant M5_pid field from processBrandon Potter
2016-11-09style: [patch 3/22] reduce include dependencies in some headersBrandon Potter
Used cppclean to help identify useless includes and removed them. This involved erroneously included headers, but also cases where forward declarations could have been used rather than a full include.
2016-11-09syscall_emul: [patch 2/22] move SyscallDesc into its own .hh and .ccBrandon Potter
The class was crammed into syscall_emul.hh which has tons of forward declarations and template definitions. To clean it up a bit, moved the class into separate files and commented the class with doxygen style comments. Also, provided some encapsulation by adding some accessors and a mutator. The syscallreturn.hh file was renamed syscall_return.hh to make it consistent with other similarly named files in the src/sim directory. The DPRINTF_SYSCALL macro was moved into its own header file with the include the Base and Verbose flags as well. --HG-- rename : src/sim/syscallreturn.hh => src/sim/syscall_return.hh
2016-11-09style: [patch 1/22] use /r/3648/ to reorganize includesBrandon Potter
2016-12-23sim: Fix SE mode checkpoint restore file handlingJoel Hestness
When restoring from a checkpoint, the simulation used to use file handles from the checkpoint. This disallows multiple separate restore simulations from using separate input and output files and directories, and plays havoc when the checkpointed file locations may have changed. Add handling to allow the command line specified files to be used as input/output for the restored simulation (Note: this is the similar functionality to FS mode for output and error).
2016-11-30arch: [Patch 1/5] Added RISC-V base instruction set RV64IAlec Roelke
First of five patches adding RISC-V to GEM5. This patch introduces the base 64-bit ISA (RV64I) in src/arch/riscv for use with syscall emulation. The multiply, floating point, and atomic memory instructions will be added in additional patches, as well as support for more detailed CPU models. The loader is also modified to be able to parse RISC-V ELF files, and a "Hello world\!" example for RISC-V is added to test-progs. Patch 2 will implement the multiply extension, RV64M; patch 3 will implement the floating point (single- and double-precision) extensions, RV64FD; patch 4 will implement the atomic memory instructions, RV64A, and patch 5 will add support for timing, minor, and detailed CPU models that is missing from the first four patches (such as handling locked memory). [Removed several unused parameters and imports from RiscvInterrupts.py, RiscvISA.py, and RiscvSystem.py.] [Fixed copyright information in RISC-V files copied from elsewhere that had ARM licenses attached.] [Reorganized instruction definitions in decoder.isa so that they are sorted by opcode in preparation for the addition of ISA extensions M, A, F, D.] [Fixed formatting of several files, removed some variables and instructions that were missed when moving them to other patches, fixed RISC-V Foundation copyright attribution, and fixed history of files copied from other architectures using hg copy.] [Fixed indentation of switch cases in isa.cc.] [Reorganized syscall descriptions in linux/process.cc to remove large number of repeated unimplemented system calls and added implmementations to functions that have received them since it process.cc was first created.] [Fixed spacing for some copyright attributions.] [Replaced the rest of the file copies using hg copy.] [Fixed style check errors and corrected unaligned memory accesses.] [Fix some minor formatting mistakes.] Signed-off by: Alec Roelke Signed-off by: Jason Lowe-Power <jason@lowepower.com>
2016-11-17alpha: Remove ALPHA tru64 support and associated testsAndreas Hansson
No one appears to be using it, and it is causing build issues and increases the development and maintenance effort.
2016-06-06sim: Call regStats of base-class as wellStephan Diestelhorst
We want to extend the stats of objects hierarchically and thus it is necessary to register the statistics of the base-class(es), as well. For now, these are empty, but generic stats will be added there. Patch originally provided by Akash Bagdia at ARM Ltd.
2016-03-17base: add symbol support for dynamic librariesBrandon Potter
Libraries are loaded into the process address space using the mmap system call. Conveniently, this happens to be a good time to update the process symbol table with the library's incoming symbols so we handle the table update from within the system call. This works just like an application's normal symbols. The only difference between a dynamic library and a main executable is when the symbol table update occurs. The symbol table update for an executable happens at program load time and is finished before the process ever begins executing. Since dynamic linking happens at runtime, the symbol loading happens after the library is first loaded into the process address space. The library binary is examined at this time for a symbol section and that section is parsed for symbol types with specific bindings (global, local, weak). Subsequently, these symbols are added to the table and are available for use by gem5 for things like trace generation. Checkpointing should work just as it did previously. The address space (and therefore the library) will be recorded and the symbol table will be entirely recorded. (It's not possible to do anything clever like checkpoint a program and then load the program back with different libraries with LD_LIBRARY_PATH, because the library becomes part of the address space after being loaded.)
2016-03-17base: support dynamic loading of Linux ELF objects in SE modeBrandon Potter
2016-03-17syscall_emul: move mmapGrowsDown() to LiveProcessSteve Reinhardt
The mmapGrowsDown() method was a static method on the OperatingSystem class (and derived classes), which worked OK for the templated syscall emulation methods, but made it hard to access elsewhere. This patch moves the method to be a virtual function on the LiveProcess method, where it can be overridden for specific platforms (for now, Alpha). This patch also changes the value of mmapGrowsDown() from being false by default and true only on X86Linux32 to being true by default and false only on Alpha, which seems closer to reality (though in reality most people use ASLR and this doesn't really matter anymore). In the process, also got rid of the unused mmap_start field on LiveProcess and OperatingSystem mmapGrowsUp variable.
2016-03-17syscall_emul, style: fix newline issue inside assertBrandon Potter
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.
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.
2015-09-29syscall_emul: Bandage readlink /proc/self/exeJoel Hestness
The recent changeset to readlink() to handle reading the /proc/self/exe link introduces a number of problems. This patch fixes two: 1) Because readlink() called on /proc/self/exe now uses LiveProcess::progName() to find the binary path, it will only get the zeroth parameter of the simulated system command line. However, if a config script also specifies the process' executable, the executable parameter is used to create the LiveProcess rather than the zeroth command line parameter. Thus, the zeroth command line parameter is not necessarily the correct path to the binary executing in the simulated system. To fix this, add a LiveProcess data member, 'executable', which is correctly set during instantiation and returned from progName(). 2) If a config script allows a user to pass a relative path as the zeroth simulated system command line parameter or process executable, readlink() will incorrecly return a relative path when called on '/proc/self/exe'. /proc/self/exe is always set to a full path, so running benchmarks can fail if a relative path is returned. To fix this, clean up the handling of LiveProcess::progName() within readlink() to get the full binary path. NOTE: This patch still leaves the potential problem that host full path to the binary bleeds into the simulated system, potentially causing the appearance of non-deterministic simulated system execution.
2015-07-24style: change Process function calls to use camelCaseBrandon Potter
The Process class methods were using an improper style and this subsequently bled into the system call code. The following regular expressions should be helpful if someone transitions private system call patches on top of these changesets: s/alloc_fd/allocFD/ s/sim_fd(/simFD(/ s/sim_fd_obj/getFDEntry/ s/fix_file_offsets/fixFileOffsets/ s/find_file_offsets/findFileOffsets/
2015-07-24base: refactor process class (specifically FdMap and friends)Brandon Potter
This patch extends the previous patch's alterations around fd_map. It cleans up some of the uglier code in the process file and replaces it with a more concise C++11 version. As part of the changes, the FdMap class is pulled out of the Process class and receives its own file.
2015-07-24syscall_emul: file descriptor interface changesBrandon Potter
This patch gets rid of unused Process::dup_fd method and does minor refactoring in the process class files. The file descriptor max has been changed to be the number of file descriptors since this clarifies the loop boundary condition and cleans up the code a bit. The fd_map field has been altered to be dynamically allocated as opposed to being an array; the intention here is to build on this is subsequent patches to allow processes to share their file descriptors with the clone system call.
2015-07-07sim: Refactor and simplify the drain APIAndreas Sandberg
The drain() call currently passes around a DrainManager pointer, which is now completely pointless since there is only ever one global DrainManager in the system. It also contains vestiges from the time when SimObjects had to keep track of their child objects that needed draining. This changeset moves all of the DrainState handling to the Drainable base class and changes the drain() and drainResume() calls to reflect this. Particularly, the drain() call has been updated to take no parameters (the DrainManager argument isn't needed) and return a DrainState instead of an unsigned integer (there is no point returning anything other than 0 or 1 any more). Drainable objects should return either DrainState::Draining (equivalent to returning 1 in the old system) if they need more time to drain or DrainState::Drained (equivalent to returning 0 in the old system) if they are already in a consistent state. Returning DrainState::Running is considered an error. Drain done signalling is now done through the signalDrainDone() method in the Drainable class instead of using the DrainManager directly. The new call checks if the state of the object is DrainState::Draining before notifying the drain manager. This means that it is safe to call signalDrainDone() without first checking if the simulator has requested draining. The intention here is to reduce the code needed to implement draining in simple objects.
2015-07-07sim: Refactor the serialization base classAndreas Sandberg
Objects that are can be serialized are supposed to inherit from the Serializable class. This class is meant to provide a unified API for such objects. However, so far it has mainly been used by SimObjects due to some fundamental design limitations. This changeset redesigns to the serialization interface to make it more generic and hide the underlying checkpoint storage. Specifically: * Add a set of APIs to serialize into a subsection of the current object. Previously, objects that needed this functionality would use ad-hoc solutions using nameOut() and section name generation. In the new world, an object that implements the interface has the methods serializeSection() and unserializeSection() that serialize into a named /subsection/ of the current object. Calling serialize() serializes an object into the current section. * Move the name() method from Serializable to SimObject as it is no longer needed for serialization. The fully qualified section name is generated by the main serialization code on the fly as objects serialize sub-objects. * Add a scoped ScopedCheckpointSection helper class. Some objects need to serialize data structures, that are not deriving from Serializable, into subsections. Previously, this was done using nameOut() and manual section name generation. To simplify this, this changeset introduces a ScopedCheckpointSection() helper class. When this class is instantiated, it adds a new /subsection/ and subsequent serialization calls during the lifetime of this helper class happen inside this section (or a subsection in case of nested sections). * The serialize() call is now const which prevents accidental state manipulation during serialization. Objects that rely on modifying state can use the serializeOld() call instead. The default implementation simply calls serialize(). Note: The old-style calls need to be explicitly called using the serializeOld()/serializeSectionOld() style APIs. These are used by default when serializing SimObjects. * Both the input and output checkpoints now use their own named types. This hides underlying checkpoint implementation from objects that need checkpointing and makes it easier to change the underlying checkpoint storage code.
2015-04-29arch, base, dev, kern, sym: FreeBSD supportRuslan Bukin
This adds support for FreeBSD/aarch64 FS and SE mode (basic set of syscalls only) Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2015-04-13sim: Use NULL instead of None for testing filenames.Nilay Vaish
The filenames are initialized with NULL. So the test should be checking for them to be == NULL instead == None.
2014-11-24misc: Another round of static analysis fixupsAndreas Hansson
Mostly addressing uninitialised members.
2014-11-23mem: Page Table map api modificationAlexandru Dutu
This patch adds uncacheable/cacheable and read-only/read-write attributes to the map method of PageTableBase. It also modifies the constructor of TlbEntry structs for all architectures to consider the new attributes.
2014-11-23x86: Segment initialization to support KvmCPU in SEAlexandru Dutu
This patch sets up low and high privilege code and data segments and places them in the following order: cs low, ds low, ds, cs, in the GDT. Additionally, a syscall and page fault handler for KvmCPU in SE mode are defined. The order of the segment selectors in GDT is required in this manner for interrupt handling to work properly. Segment initialization is done for all the thread contexts.
2014-10-22syscall_emul: minor style fix to LiveProcess constructorSteve Reinhardt
2014-10-22syscall_emul: add EmulatedDriver objectSteve Reinhardt
Fake SE-mode device drivers can now be added by deriving from this abstract object.
2014-09-20alpha,arm,mips,power,x86,cpu,sim: Cleanup activate/deactivateMitch Hayenga
activate(), suspend(), and halt() used on thread contexts had an optional delay parameter. However this parameter was often ignored. Also, when used, the delay was seemily arbitrarily set to 0 or 1 cycle (no other delays were ever specified). This patch removes the delay parameter and 'Events' associated with them across all ISAs and cores. Unused activate logic is also removed.
2014-09-03arch: Cleanup unused ISA traits constantsAndreas Hansson
This patch prunes unused values, and also unifies how the values are defined (not using an enum for ALPHA), aligning the use of int vs Addr etc. The patch also removes the duplication of PageBytes/PageShift and VMPageSize/LogVMPageSize. For all ISAs the two pairs had identical values and the latter has been removed.
2014-08-28mem: adding architectural page table support for SE modeAlexandru
This patch enables the use of page tables that are stored in system memory and respect x86 specification, in SE mode. It defines an architectural page table for x86 as a MultiLevelPageTable class and puts a placeholder class for other ISAs page tables, giving the possibility for future implementation.
2014-04-01mem: adding a multi-level page table classAlexandru
This patch defines a multi-level page table class that stores the page table in system memory, consistent with ISA specifications. In this way, cpu models that use the actual hardware to execute (e.g. KvmCPU), are able to traverse the page table.
2014-01-24arm: Add support for ARMv8 (AArch64 & AArch32)ARM gem5 Developers
Note: AArch64 and AArch32 interworking is not supported. If you use an AArch64 kernel you are restricted to AArch64 user-mode binaries. This will be addressed in a later patch. Note: Virtualization is only supported in AArch32 mode. This will also be fixed in a later patch. Contributors: Giacomo Gabrielli (TrustZone, LPAE, system-level AArch64, AArch64 NEON, validation) Thomas Grocutt (AArch32 Virtualization, AArch64 FP, validation) Mbou Eyole (AArch64 NEON, validation) Ali Saidi (AArch64 Linux support, code integration, validation) Edmund Grimley-Evans (AArch64 FP) William Wang (AArch64 Linux support) Rene De Jong (AArch64 Linux support, performance opt.) Matt Horsnell (AArch64 MP, validation) Matt Evans (device models, code integration, validation) Chris Adeniyi-Jones (AArch64 syscall-emulation) Prakash Ramrakhyani (validation) Dam Sunwoo (validation) Chander Sudanthi (validation) Stephan Diestelhorst (validation) Andreas Hansson (code integration, performance opt.) Eric Van Hensbergen (performance opt.) Gabe Black
2013-04-17base: load weak symbols from object fileDeyuan Guo ext:(%2C%20Nilay%20Vaish%20%3Cnilay%40cs.wisc.edu%3E)
Without loading weak symbols into gem5, some function names and the given PC cannot correspond correctly, because the binding attributes of unction names in an ELF file are not only STB_GLOBAL or STB_LOCAL, but also STB_WEAK. This patch adds a function for loading weak symbols. Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2013-03-02sim: remove duplicate check on stack sizeNilay Vaish
2013-02-19scons: Fix up numerous warnings about name shadowingAndreas Hansson
This patch address the most important name shadowing warnings (as produced when using gcc/clang with -Wshadow). There are many locations where constructor parameters and function parameters shadow local variables, but these are left unchanged.
2012-08-28Clock: Add a Cycles wrapper class and use where applicableAndreas Hansson
This patch addresses the comments and feedback on the preceding patch that reworks the clocks and now more clearly shows where cycles (relative cycle counts) are used to express time. Instead of bumping the existing patch I chose to make this a separate patch, merely to try and focus the discussion around a smaller set of changes. The two patches will be pushed together though. This changes done as part of this patch are mostly following directly from the introduction of the wrapper class, and change enough code to make things compile and run again. There are definitely more places where int/uint/Tick is still used to represent cycles, and it will take some time to chase them all down. Similarly, a lot of parameters should be changed from Param.Tick and Param.Unsigned to Param.Cycles. In addition, the use of curTick is questionable as there should not be an absolute cycle. Potential solutions can be built on top of this patch. There is a similar situation in the o3 CPU where lastRunningCycle is currently counting in Cycles, and is still an absolute time. More discussion to be had in other words. An additional change that would be appropriate in the future is to perform a similar wrapping of Tick and probably also introduce a Ticks class along with suitable operators for all these classes.