gem5 - gem5

Age	Commit message (Collapse)	Author
2013-09-30	kvm: Add support for thread-specific instruction events	Andreas Sandberg
	Instruction events are currently ignored when executing in KVM. This changeset adds support for triggering KVM exits based on instruction counts using hardware performance counters. Depending on the underlying performance counter implementation, there might be some inaccuracies due to instructions being counted in the host kernel when entering/exiting KVM. Due to limitations/bugs in Linux's performance counter interface, we can't reliably change the period of an overflow counter. We work around this issue by detaching and reattaching the counter if we need to reconfigure it.
2013-06-11	kvm: Add more VM stats	Andreas Sandberg
	This changeset adds the following stats to KVM: * numVMHalfEntries: Number of entries into KVM to finalize pending IO operations without executing guest instructions. These typically happen as a result of a drain where the guest must finalize some operations before the guest state is consistent. * numExitSignal: Number of VM exits that have been triggered by a signal. These usually happen as a result of the timer that limits the time spent in KVM.
2013-06-11	kvm: Separate host frequency from simulated CPU frequency	Andreas Sandberg
	We used to use the KVM CPU's clock to specify the host frequency. This was not ideal for several reasons. One of them being that the clock parameter of a CPU determines the frequency of some of the components connected to the CPU. This changeset adds a separate hostFreq parameter that should be used to specify the host frequency until we add code to autodetect it. The hostFactor should still be used to specify the conversion factor between the host performance and that of the simulated system.
2013-06-11	kvm: Don't handle IO and execute in the same tick	Andreas Sandberg
	We currently execute instructions in the guest and then handle any IO request right after we break out of the virtualized environment. This has the effect of executing IO requests in the exact same tick as the first instruction in the sequence that was just run. There seem to be cases where this simplification upsets some timing-sensitive devices. This changeset splits execute and IO (and other services) across multiple ticks. This is implemented by adding a separate RunningService state to the CPU state machine. When a VM requires service, it enters into this state and pending IO is then serviced in the future instead of immediately. The delay between getting the request and servicing it depends on the number of cycles executed in the guest, which allows other components to catch up with the CPU.
2013-06-11	kvm: Maintain a local instruction counter and update totalNumInsts	Andreas Sandberg
	Update the system's totalNumInst counter when exiting from KVM and maintain an internal absolute instruction count instead of relying on the one from perf.
2013-06-03	kvm: Allow architectures to override the cycle accounting mechanism	Andreas Sandberg
	Some architectures have special registers in the guest that can be used to do cycle accounting. This is generally preferrable since the prevents the guest from seeing a non-monotonic clock. This changeset adds a virtual method, getHostCycles(), that the architecture-specific code can override to implement this functionallity. The default implementation uses the hwCycles counter.
2013-05-14	kvm: Fix the memory interface used by KVM	Andreas Sandberg
	The CpuPort class was removed before the KVM patches were committed, which means that the KVM interface currently doesn't compile. This changeset adds the BaseKvmCPU::KVMCpuPort class which derives from MasterPort. This class is used on the data and instruction ports instead of the old CpuPort.
2013-05-02	kvm: Add a stat counting number of instructions executed	Andreas Sandberg
	This changeset adds a 'numInsts' stat to the KVM-based CPU. It also cleans up the variable names in kvmRun to make the distinction between host cycles and estimated simulated cycles clearer. As a bonus feature, it also fixes a warning (unreferenced variable) when compiling in fast mode.
2013-04-22	kvm: Add experimental support for a perf-based execution timer	Andreas Sandberg
	Add support for using the CPU cycle counter instead of a normal POSIX timer to generate timed exits to gem5. This should, in theory, provide better resolution when requesting timer signals. The perf-based timer requires a fairly recent kernel since it requires a working PERF_EVENT_IOC_PERIOD ioctl. This ioctl has existed in the kernel for a long time, but it used to be completely broken due to an inverted match when the kernel copied things from user space. Additionally, the ioctl does not change the sample period correctly on all kernel versions which implement it. It is currently only known to work reliably on kernel version 3.7 and above on ARM.
2013-04-22	kvm: Avoid synchronizing the TC on every KVM exit	Andreas Sandberg
	Reduce the number of KVM->TC synchronizations by overloading the getContext() method and only request an update when the TC is requested as opposed to every time KVM returns to gem5.
2013-04-22	kvm: Basic support for hardware virtualized CPUs	Andreas Sandberg
	This changeset introduces the architecture independent parts required to support KVM-accelerated CPUs. It introduces two new simulation objects: KvmVM -- The KVM VM is a component shared between all CPUs in a shared memory domain. It is typically instantiated as a child of the system object in the simulation hierarchy. It provides access to KVM VM specific interfaces. BaseKvmCPU -- Abstract base class for all KVM-based CPUs. Architecture dependent CPU implementations inherit from this class and implement the following methods: * updateKvmState() -- Update the architecture-dependent KVM state from the gem5 thread context associated with the CPU. * updateThreadContext() -- Update the thread context from the architecture-dependent KVM state. * dump() -- Dump the KVM state using (optional). In order to deliver interrupts to the guest, CPU implementations typically override the tick() method and check for, and deliver, interrupts prior to entering KVM. Hardware-virutalized CPU currently have the following limitations: * SE mode is not supported. * PC events are not supported. * Timing statistics are currently very limited. The current approach simply scales the host cycles with a user-configurable factor. * The simulated system must not contain any caches. * Since cycle counts are approximate, there is no way to request an exact number of cycles (or instructions) to be executed by the CPU. * Hardware virtualized CPUs and gem5 CPUs must not execute at the same time in the same simulator instance. * Only single-CPU systems can be simulated. * Remote GDB connections to the guest system are not supported. Additionally, m5ops requires an architecture specific interface and might not be supported.