summaryrefslogtreecommitdiff
path: root/src/mem/cache
AgeCommit message (Collapse)Author
2014-12-23mem: Hide WriteInvalidate requests from prefetchersCurtis Dunham
Without this tweak, a prefetcher will happily prefetch data that will promptly be invalidated and overwritten by a WriteInvalidate.
2014-12-23mem: Fix event scheduling issue for prefetchesMitch Hayenga
The cache's MemSidePacketQueue schedules a sendEvent based upon nextMSHRReadyTime() which is the time when the next MSHR is ready or whenever a future prefetch is ready. However, a prefetch being ready does not guarentee that it can obtain an MSHR. So, when all MSHRs are full, the simulation ends up unnecessiciarly scheduling a sendEvent every picosecond until an MSHR is finally freed and the prefetch can happen. This patch fixes this by not signaling the prefetch ready time if the prefetch could not be generated. The event is rescheduled as soon as a MSHR becomes available.
2014-12-23mem: Fix bug relating to writebacks and prefetchesMitch Hayenga
Previously the code commented about an unhandled case where it might be possible for a writeback to arrive after a prefetch was generated but before it was sent to the memory system. I hit that case. Luckily the prefetchSquash() logic already in the code handles dropping prefetch request in certian circumstances.
2014-12-23mem: Rework the structuring of the prefetchersMitch Hayenga
Re-organizes the prefetcher class structure. Previously the BasePrefetcher forced multiple assumptions on the prefetchers that inherited from it. This patch makes the BasePrefetcher class truly representative of base functionality. For example, the base class no longer enforces FIFO order. Instead, prefetchers with FIFO requests (like the existing stride and tagged prefetchers) now inherit from a new QueuedPrefetcher base class. Finally, the stride-based prefetcher now assumes a custimizable lookup table (sets/ways) rather than the previous fully associative structure.
2014-12-23mem: Add parameter to reserve MSHR entries for demand accessMitch Hayenga
Adds a new parameter that reserves some number of MSHR entries for demand accesses. This helps prevent prefetchers from taking all MSHRs, forcing demand requests from the CPU to stall.
2014-12-02mem: Support WriteInvalidate (again)Curtis Dunham
This patch takes a clean-slate approach to providing WriteInvalidate (write streaming, full cache line writes without first reading) support. Unlike the prior attempt, which took an aggressive approach of directly writing into the cache before handling the coherence actions, this approach follows the existing cache flows as closely as possible.
2014-12-02mem: Remove WriteInvalidate supportCurtis Dunham
Prepare for a different implementation following in the next patch
2014-12-02mem: Clean up packet data allocationAndreas Hansson
This patch attempts to make the rules for data allocation in the packet explicit, understandable, and easy to verify. The constructor that copies a packet is extended with an additional flag "alloc_data" to enable the call site to explicitly say whether the newly created packet is short-lived (a zero-time snoop), or has an unknown life-time and therefore should allocate its own data (or copy a static pointer in the case of static data). The tricky case is the static data. In essence this is a copy-avoidance scheme where the original source of the request (DMA, CPU etc) does not ask the memory system to return data as part of the packet, but instead provides a pointer, and then the memory system carries this pointer around, and copies the appropriate data to the location itself. Thus any derived packet actually never copies any data. As the original source does not copy any data from the response packet when arriving back at the source, we must maintain the copy of the original pointer to not break the system. We might want to revisit this one day and pay the price for a few extra memcpy invocations. All in all this patch should make it easier to grok what is going on in the memory system and how data is actually copied (or not).
2014-12-02mem: Cleanup Packet::checkFunctional and hasData usageAndreas Hansson
This patch cleans up the use of hasData and checkFunctional in the packet. The hasData function is unfortunately suggesting that it checks if the packet has a valid data pointer, when it does in fact only check if the specific packet type is specified to have a data payload. The confusion led to a bug in checkFunctional. The latter function is also tidied up to avoid name overloading.
2014-12-02mem: Make the requests carried by packets constAndreas Hansson
This adds a basic level of sanity checking to the packet by ensuring that a request is not modified once the packet is created. The only issue that had to be worked around is the relaying of software-prefetches in the cache. The specific situation is now solved by first copying the request, and then creating a new packet accordingly.
2014-12-02mem: Add checks and explanation for assertMemInhibit usageAndreas Hansson
2014-12-02mem: Remove redundant Packet::allocate callsAndreas Hansson
This patch cleans up the packet memory allocation confusion. The data is always allocated at the requesting side, when a packet is created (or copied), and there is never a need for any device to allocate any space if it is merely responding to a paket. This behaviour is in line with how SystemC and TLM works as well, thus increasing interoperability, and matching established conventions. The redundant calls to Packet::allocate are removed, and the checks in the function are tightened up to make sure data is only ever allocated once. There are still some oddities in the packet copy constructor where we copy the data pointer if it is static (without ownership), and allocate new space if the data is dynamic (with ownership). The latter is being worked on further in a follow-on patch.
2014-12-02mem: Add const getters for write packet dataAndreas Hansson
This patch takes a first step in tightening up how we use the data pointer in write packets. A const getter is added for the pointer itself (getConstPtr), and a number of member functions are also made const accordingly. In a range of places throughout the memory system the new member is used. The patch also removes the unused isReadWrite function.
2014-10-29arm, mem: Fix drain bug and provide drain prints for more components.Ali Saidi
2014-10-21mem: don't inhibit WriteInv's or defer snoops on their MSHRsCurtis Dunham
WriteInvalidate semantics depend on the unconditional writeback or they won't complete. Also, there's no point in deferring snoops on their MSHRs, as they don't get new data at the end of their life cycle the way other transactions do. Add comment in the cache about a minor inefficiency re: WriteInvalidate.
2014-10-29mem: have WriteInvalidate obsolete MSHRsCurtis Dunham
Since WriteInvalidate directly writes into the cache, it can create tricky timing interleavings with reads and writes to the same cache line that haven't yet completed. This patch ensures that these requests, when completed, don't overwrite the newer data from the WriteInvalidate.
2014-10-16mem: Dynamically determine page bytes in memory componentsAndreas Hansson
This patch takes a step towards an ISA-agnostic memory system by enabling the components to establish the page size after instantiation. The swap operation in the memory is now also allowing any granularity to avoid depending on the IntReg of the ISA.
2014-10-09mem: Add packet sanity checks to cache and MSHRsAndreas Hansson
This patch adds a number of asserts to the cache, checking basic assumptions about packets being requests or responses.
2014-09-27misc: Fix a bunch of minor issues identified by static analysisAndreas Hansson
Add some missing initialisation, and fix a handful benign resource leaks (including some false positives).
2014-09-20mem: Rename Bus to XBar to better reflect its behaviourAndreas Hansson
This patch changes the name of the Bus classes to XBar to better reflect the actual timing behaviour. The actual instances in the config scripts are not renamed, and remain as e.g. iobus or membus. As part of this renaming, the code has also been clean up slightly, making use of range-based for loops and tidying up some comments. The only changes outside the bus/crossbar code is due to the delay variables in the packet. --HG-- rename : src/mem/Bus.py => src/mem/XBar.py rename : src/mem/coherent_bus.cc => src/mem/coherent_xbar.cc rename : src/mem/coherent_bus.hh => src/mem/coherent_xbar.hh rename : src/mem/noncoherent_bus.cc => src/mem/noncoherent_xbar.cc rename : src/mem/noncoherent_bus.hh => src/mem/noncoherent_xbar.hh rename : src/mem/bus.cc => src/mem/xbar.cc rename : src/mem/bus.hh => src/mem/xbar.hh
2014-09-20mem: Remove the GHB prefetcher from the source treeMitch Hayenga
There are two primary issues with this code which make it deserving of deletion. 1) GHB is a way to structure a prefetcher, not a definitive type of prefetcher 2) This prefetcher isn't even structured like a GHB prefetcher. It's basically a worse version of the stride prefetcher. It primarily serves to confuse new gem5 users and most functionality is already present in the stride prefetcher.
2014-09-19misc: Remove assertions ensuring unsigned values >= 0Andreas Hansson
2014-09-19mem: Add checks to sendTimingReq in cacheAndreas Hansson
A small fix to ensure the return value is not ignored.
2014-09-09misc: Fix a number of unitialised variables and membersAndreas Hansson
Static analysis unearther a bunch of uninitialised variables and members, and this patch addresses the problem. In all cases these omissions seem benign in the end, but at least fixing them means less false positives next time round.
2014-06-27mem: write streaming support via WriteInvalidate promotionCurtis Dunham
Support full-block writes directly rather than requiring RMW: * a cache line is allocated in the cache upon receipt of a WriteInvalidateReq, not the WriteInvalidateResp. * only top-level caches allocate the line; the others just pass the request along and invalidate as necessary. * to close a timing window between the *Req and the *Resp, a new metadata bit tracks whether another cache has read a copy of the new line before the writeback to memory.
2014-09-03mem: Fix a bug in the cache port flow controlAndreas Hansson
This patch fixes a bug in the cache port where the retry flag was reset too early, allowing new requests to arrive before the retry was actually sent, but with the event already scheduled. This caused a deadlock in the interactions with the O3 LSQ. The patche fixes the underlying issue by shifting the resetting of the flag to be done by the event that also calls sendRetry(). The patch also tidies up the flow control in recvTimingReq and ensures that we also check if we already have a retry outstanding.
2014-05-13cpu, mem: Make software prefetches non-blockingCurtis Dunham
Previously, they were treated so much like loads that they could stall at the head of the ROB. Now they are always treated like L1 hits. If they actually miss, a new request is created at the L1 and tracked from the MSHRs there if necessary (i.e. if it didn't coalesce with an existing outstanding load).
2014-09-03cache: Fix handling of LL/SC requests under contentionGeoffrey Blake
If a set of LL/SC requests contend on the same cache block we can get into a situation where CPUs will deadlock if they expect a failed SC to supply them data. This case happens where 3 or more cores are contending for a cache block using LL/SC and the system is configured where 2 cores are connected to a local bus and the third is connected to a remote bus. If a core on the local bus sends an SCUpgrade and the core on the remote bus sends and SCUpgrade they will race to see who will win the SC access. In the meantime if the other core appends a read to one of the SCUpgrades it will expect to be supplied data by that SCUpgrade transaction. If it happens that the SCUpgrade that was picked to supply the data is failed, it will drop the appended request for data and never respond, leaving the requesting core to deadlock. This patch makes all SC's behave as normal stores to prevent this case but still makes sure to check whether it can perform the update.
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.
2014-08-13mem: Properly set cache block status fields on writebacksMitch Hayenga
When a cacheline is written back to a lower-level cache, tags->insertBlock() sets various status parameters. However these status bits were cleared immediately after calling. This patch makes it so that these status fields are not cleared by moving them outside of the tags->insertBlock() call.
2014-07-28mem: refactor LRU cache tags and add random replacement tagsAnthony Gutierrez
this patch implements a new tags class that uses a random replacement policy. these tags prefer to evict invalid blocks first, if none are available a replacement candidate is chosen at random. this patch factors out the common code in the LRU class and creates a new abstract class: the BaseSetAssoc class. any set associative tag class must implement the functionality related to the actual replacement policy in the following methods: accessBlock() findVictim() insertBlock() invalidate()
2014-05-09mem: Squash prefetch requests from downstream cachesMitch Hayenga
This patch squashes prefetch requests from downstream caches, so that they do not steal cachelines away from caches closer to the cpu. It was originally coded by Mitch Hayenga and modified by Aasheesh Kolli.
2014-04-01mem: Don't print out the data of a cache blockMitch Hayenga
This never actually worked since it was printing out only a word of the cache block and not the entire thing and doubly didn't work csprintf overrides the %#x specifier and assumes a char* array is actually a string.
2014-03-07mem: Fix incorrect assert failure in the CachePrakash Ramrakhyani
This patch fixes an assert condition that is not true at all times. There are valid situations that arise in dual-core dual-workload runs where the assert condition is false. The function call following the assert however needs to be called only when the condition is true (a block cannot be invalidated in the tags structure if has not been allocated in the structure, and the tempBlock is never allocated). Hence the 'assert' has been replaced with an 'if'.
2014-02-18mem: Filter cache snoops based on address rangesAndreas Hansson
This patch adds a filter to the cache to drop snoop requests that are not for a range covered by the cache. This fixes an issue observed when multiple caches are placed in parallel, covering different address ranges. Without this patch, all the caches will forward the snoop upwards, when only one should do so.
2014-01-29mem: Add additional tolerance to stride prefetcherMitch Hayenga
Forces the prefetcher to mispredict twice in a row before resetting the confidence of prefetching. This helps cases where a load PC strides by a constant factor, however it may operate on different arrays at times. Avoids the cost of retraining. Primarily helps with small iteration loops. Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2014-01-29mem: Allowed tagged instruction prefetching in stride prefetcherMitch Hayenga
For systems with a tightly coupled L2, a stride-based prefetcher may observe access requests from both instruction and data L1 caches. However, the PC address of an instruction miss gives no relevant training information to the stride based prefetcher(there is no stride to train). In theses cases, its better if the L2 stride prefetcher simply reverted back to a simple N-block ahead prefetcher. This patch enables this option. Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2014-01-29mem: prefetcher: add options, support for unaligned addressesMitch Hayenga ext:(%2C%20Amin%20Farmahini%20%3Caminfar%40gmail.com%3E)
This patch extends the classic prefetcher to work on non-block aligned addresses. Because the existing prefetchers in gem5 mask off the lower address bits of cache accesses, many predictable strides fail to be detected. For example, if a load were to stride by 48 bytes, with 64 byte cachelines, the current stride based prefetcher would see an access pattern of 0, 64, 64, 128, 192.... Thus not detecting a constant stride pattern. This patch fixes this, by training the prefetcher on access and not masking off the lower address bits. It also adds the following configuration options: 1) Training/prefetching only on cache misses, 2) Training/prefetching only on data acceses, 3) Optionally tagging prefetches with a PC address. #3 allows prefetchers to train off of prefetch requests in systems with multiple cache levels and PC-based prefetchers present at multiple levels. It also effectively allows a pipelining of prefetch requests (like in POWER4) across multiple levels of cache hierarchy. Improves performance on my gem5 configuration by 4.3% for SPECINT and 4.7% for SPECFP (geomean).
2014-01-28mem: Remove redundant findVictim() input argumentAmin Farmahini
The patch (1) removes the redundant writeback argument from findVictim() (2) fixes the description of access() function Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2014-01-24mem: Add support for a security bit in the memory systemGiacomo Gabrielli
This patch adds the basic building blocks required to support e.g. ARM TrustZone by discerning secure and non-secure memory accesses.
2014-01-24Cache: Collect very basic stats on tag and data accessesTimothy M. Jones
Adds very basic statistics on the number of tag and data accesses within the cache, which is important for power modelling. For the tags, simply count the associativity of the cache each time. For the data, this depends on whether tags and data are accessed sequentially, which is given by a new parameter. In the parallel case, all data blocks are accessed each time, but with sequential accesses, a single data block is accessed only on a hit.
2014-01-24mem: per-thread cache occupancy and per-block agesDam Sunwoo
This patch enables tracking of cache occupancy per thread along with ages (in buckets) per cache blocks. Cache occupancy stats are recalculated on each stat dump.
2014-01-24mem: track per-request latencies and access depths in the cache hierarchyMatt Horsnell
Add some values and methods to the request object to track the translation and access latency for a request and which level of the cache hierarchy responded to the request.
2013-10-17cpu: add consistent guarding to *_impl.hh files.Matt Horsnell
2013-09-04arch: Resurrect the NOISA build target and rename it NULLAndreas Hansson
This patch makes it possible to once again build gem5 without any ISA. The main purpose is to enable work around the interconnect and memory system without having to build any CPU models or device models. The regress script is updated to include the NULL ISA target. Currently no regressions make use of it, but all the testers could (and perhaps should) transition to it. --HG-- rename : build_opts/NOISA => build_opts/NULL rename : src/arch/noisa/SConsopts => src/arch/null/SConsopts rename : src/arch/noisa/cpu_dummy.hh => src/arch/null/cpu_dummy.hh rename : src/cpu/intr_control.cc => src/cpu/intr_control_noisa.cc
2013-07-18mem: Set the cache line size on a system levelAndreas Hansson
This patch removes the notion of a peer block size and instead sets the cache line size on the system level. Previously the size was set per cache, and communicated through the interconnect. There were plenty checks to ensure that everyone had the same size specified, and these checks are now removed. Another benefit that is not yet harnessed is that the cache line size is now known at construction time, rather than after the port binding. Hence, the block size can be locally stored and does not have to be queried every time it is used. A follow-on patch updates the configuration scripts accordingly.
2013-07-18mem: Add cache class destructor to avoid memory leaksXiangyu Dong
Make valgrind a little bit happier
2013-06-27mem: Reorganize cache tags and make them a SimObjectPrakash Ramrakhyani
This patch reorganizes the cache tags to allow more flexibility to implement new replacement policies. The base tags class is now a clocked object so that derived classes can use a clock if they need one. Also having deriving from SimObject allows specialized Tag classes to be swapped in/out in .py files. The cache set is now templatized to allow it to contain customized cache blocks with additional informaiton. This involved moving code to the .hh file and removing cacheset.cc. The statistics belonging to the cache tags are now including ".tags" in their name. Hence, the stats need an update to reflect the change in naming.
2013-06-27mem: Remove the cache builderAndreas Hansson
This patch removes the redundant cache builder class.
2013-06-27mem: Align cache timing to clock edgesAndreas Hansson
This patch changes the cache timing calculations such that the results are aligned to clock edges. Plenty stats change as a results of this patch.