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Note current PRFM supports only PLD, but PST (prefetch for store) is
also important for latency hiding. We also bug fix in disassembler to
display prfop correctly.
Change-Id: I9144e7233900aa2d555e1c1a6a2c2e41d837aa13
Signed-off-by: Yuetsu Kodama <yuetsu.kodama@riken.jp>
Reviewed-on: https://gem5-review.googlesource.com/c/13675
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
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This patch changes how we deal with whole-line writes their
responses. With these changes, we use the MSHR tracking to determine
if a whole-line is written, and on a fill we simply handle the
invalidation response, with the actual writes taking place as part of
satisfying the CPU-side hit.
Change-Id: I9a18e41a95db3c20b97f8bca7d95ff33d35a578b
Reviewed-on: https://gem5-review.googlesource.com/c/12905
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
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Change-Id: Iebefeb5b1ce905f2b45b30b7656d6a01d0724584
Reviewed-on: https://gem5-review.googlesource.com/c/13575
Maintainer: Gabe Black <gabeblack@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
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The NULL ISA doesn't really have an endianness. Now that the packet
accessors which consumed that endianness are gone, we can get rid of
that setting as well.
Change-Id: I8dd4c7b8236b07df4458fea377865f30141121d4
Reviewed-on: https://gem5-review.googlesource.com/c/13466
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
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These were left in by mistake when refactoring patches for review.
Change-Id: I4c39b5a3e2a2d3957e725a6ffcf48c25b8a69f2e
Reviewed-on: https://gem5-review.googlesource.com/c/13495
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
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This avoids a place where data has its endianness switched so that when
the endianness based accessors switch it back it returns to normal. It
also makes it easier to show intent when accessing single bytes where
endianness doesn't matter, and there's no contextual endianness.
Change-Id: I1b97396c1b9bb39727d35112d90e3969e5fe0aab
Reviewed-on: https://gem5-review.googlesource.com/c/13455
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
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This is the implementation of QoS algorithms support for gem5 memory
objects. This change-list provides a framework for specifying QoS
algorithm which can be used to prioritise service to specific masters in
the memory controller.
The QoS support implemented here is designed to be extendable so that
new QoS algorithms can be easily plugged into the memory controller as
"QoS Policies".
Change-Id: I0b611f13fce54dd1dd444eb806f8e98afd248bd5
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/11970
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
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Packet::checkFunctional also wrote data to/from the packet depending
on if it was read/write, respectively, which the 'check' in the name
would suggest otherwise. This renames it to doFunctional, which is
more suggestive. It also renames any function called checkFunctional
which calls Packet::checkFunctional. These are
- Bridge::BridgeMasterPort::checkFunctional
- calls Packet::checkFunctional
- MSHR::checkFunctional
- calls Packet::checkFunctional
- MSHR::TargetList::checkFunctional
- calls Packet::checkFunctional
- Queue<>::checkFunctional
(of src/mem/cache/queue.hh, not src/cpu/minor/buffers.h)
- Instantiated with Queue<WriteQueueEntry> and Queue<MSHR>
- WriteQueueEntry
- calls Packet::checkFunctional
- WriteQueueEntry::TargetList
- calls Packet::checkFunctional
- MemDelay::checkFunctional
- calls QueuedSlavePort/QueuedMasterPort::checkFunctional
- Packet::checkFunctional
- PacketQueue::checkFunctional
- calls Packet::checkFunctional
- QueuedSlavePort::checkFunctional
- calls PacketQueue::doFunctional
- QueuedMasterPort::checkFunctional
- calls PacketQueue::doFunctional
- SerialLink::SerialLinkMasterPort::checkFunctional
- calls Packet::doFunctional
Change-Id: Ieca2579c020c329040da053ba8e25820801b62c5
Reviewed-on: https://gem5-review.googlesource.com/11810
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
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AtomicOpFunctor can be used to implement atomic memory operations.
AtomicOpFunctor is captured inside a memory request and executed directly
in the memory hierarchy in a single step.
This patch enables AtomicOpFunctor pointers to be included in a memory
request and executed in a single step in the classic cache system.
This patch also makes the copy constructor of Request class do a deep
copy of AtomicOpFunctor object. This prevents a copy of a Request object
from accessing a deleted AtomicOpFunctor object.
Change-Id: I6649532b37f711e55f4552ad26893efeb300dd37
Reviewed-on: https://gem5-review.googlesource.com/8185
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
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This patch is changing the underlying type for RequestPtr from Request*
to shared_ptr<Request>. Having memory requests being managed by smart
pointers will simplify the code; it will also prevent memory leakage and
dangling pointers.
Change-Id: I7749af38a11ac8eb4d53d8df1252951e0890fde3
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/10996
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
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There are many devices that need to handle reads/writes of different
word sizes. A common pattern is a switch statement that check for the
size of a packet and then calls the corresponding
Packet::(get|set)<uintXX_t> methods. Simplify this by implementing
Packet::(get|set)UintX helper functions.
The getter reads a word of the size specified in the packet and the
specified endianness. The word is then zero-extended to 64
bits. Conversely, the setter truncates the word down to the size
required in the packet and then byte-swaps it to the desired
endianness.
Change-Id: I2f0c27fe3903abf3859bea13b07c7f5f0fb0809f
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/9761
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
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Instead of using raw memcpy, use the proper writer functions
from the Packet class in Cache.
Fixed typos in comments of these functions.
Change-Id: I156a00989c6cbaa73763349006a37a18243d6ed4
Reviewed-on: https://gem5-review.googlesource.com/9661
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
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A clean packet request serving a cache maintenance operation (CMO)
visits all memories down to the specified xbar. The visited caches
invalidate their copy (if the CMO is invalidating) and if a dirty copy
is found a write packet writes the dirty data to the memory level
below the specified xbar. A response is send back when all the caches
are clean and/or invalidated and the specified xbar has seen the write
packet.
This patch adds the following functionality in the xbar:
1) Accounts for the cache clean requests that go through the xbar
2) Generates the cache clean response when both the cache clean
request and the corresponding writeclean packet has crossed the
destination xbar.
Previously transactions in the xbar were identified using the pointer
of the original request. Cache clean transactions comprise of two
different packets, the clean request and the writeclean, and therefore
have different request pointers. This patch adds support for custom
transaction IDs that by default take the value of the request pointer
but can be overriden by the contructor. This allows the clean request
and writeclean share the same id which the coherent xbar uses to
co-ordinate them and send the response in a timely manner.
Change-Id: I80db76386a1caded38dc66e6e18f930c3bb800ff
Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5051
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
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This change adds support for maintenance operations (CMOs) in the
cache. The supported memory operations clean and/or invalidate a cache
block as specified by its VA to the specified xbar (PoU, PoC).
A cache maintenance packet visits all memories down to the specified
xbar. Caches need to invalidate their copy if it is an invalidating
CMO. If it is (additionally) a cleaning CMO and a dirty copy exists,
the cache cleans it with a WriteClean request.
Change-Id: Ibf31daa7213925898f3408738b11b1dd76c90b79
Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5049
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
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This change adds new packet cmds and request flags for cache
maintenance operations.
1) A cache clean operation writes dirty data in the first memory below
the specified xbar and updates any old copies in the memories above
it.
2) A cache invalidate operation invalidates all copies of the
specified block in the memories above the specified xbar
3) A clean and invalidate operation is a combination of the two
operations above
Change-Id: If45702848bdd568de532cd57cba58499e5e4354c
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Anouk Van Laer <anouk.vanlaer@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5047
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
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Previously, WriteClean packets would always write to the first memory
below unless the memory was unable to allocate in which case it would
be forwarded further below.
This change adds support for specifying the destination of a
WriteClean packet. The cache annotates the request with the specified
destination and marks the packet as write-through upon its
creation. The coherent xbar checks packets for their destination and
resets the write-through flag when necessary e.g., the coherent xbar
that is set as the PoC will reset the write-through flag for packets
to the PoC.
Change-Id: I84b653f5cb6e46e97e09508649a3725d72d94606
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Anouk Van Laer <anouk.vanlaer@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5046
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
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A WriteClean packet allows a cache to write a block to a memory below
without evicting its copy. A typical usecase for a WriteClean packet
is a cache clean operation.
Change-Id: If356cb067da5ddf3210c135f41ef0891fb811568
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Anouk Van Laer <anouk.vanlaer@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5044
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
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These files aren't a collection of miscellaneous stuff, they're the
definition of the Logger interface, and a few utility macros for
calling into that interface (panic, warn, etc.).
Change-Id: I84267ac3f45896a83c0ef027f8f19c5e9a5667d1
Reviewed-on: https://gem5-review.googlesource.com/6226
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Maintainer: Gabe Black <gabeblack@google.com>
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Change-Id: Ie3beeef25331f84a0a5bcc17f7a791f4a829695b
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
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This patch adds a FromCache attribute to the packet, and updates a
number of the existing request commands to reflect that the request
originates from a cache. The attribute simplifies checking if a
requests came from a cache or not, and this is used by both the cache
and snoop filter in follow-on patches.
Change-Id: Ib0a7a080bbe4d6036ddd84b46fd45bc7eb41cd8f
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Steve Reinhardt <stever@gmail.com>
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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.
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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.
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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.
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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().
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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.
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This patch adds the necessary commands and cache functionality to
allow clean writebacks. This functionality is crucial, especially when
having exclusive (victim) caches. For example, if read-only L1
instruction caches are not sending clean writebacks, there will never
be any spills from the L1 to the L2. At the moment the cache model
defaults to not sending clean writebacks, and this should possibly be
re-evaluated.
The implementation of clean writebacks relies on a new packet command
WritebackClean, which acts much like a Writeback (renamed
WritebackDirty), and also much like a CleanEvict. On eviction of a
clean block the cache either sends a clean evict, or a clean
writeback, and if any copies are still cached upstream the clean
evict/writeback is dropped. Similarly, if a clean evict/writeback
reaches a cache where there are outstanding MSHRs for the block, the
packet is dropped. In the typical case though, the clean writeback
allocates a block in the downstream cache, and marks it writable if
the evicted block was writable.
The patch changes the O3_ARM_v7a L1 cache configuration and the
default L1 caches in config/common/Caches.py
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This patch introduces the concept of a snoop latency. Given the
requirement to snoop and forward packets in zero time (due to the
coherency mechanism), the latency is accounted for later.
On a snoop, we establish the latency, and later add it to the header
delay of the packet. To allow multiple caches to contribute to the
snoop latency, we use a separate variable in the packet, and then take
the maximum before adding it to the header delay.
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This patch reverts part of (842f56345a42), as apparently there are
use-cases outside the main repository relying on the late setting of
the physical address.
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This patch simplifies the packet, and removes the possibility of
creating a packet without a valid address and/or size. Under no
circumstances are these fields set at a later point, and thus they
really have to be provided at construction time.
The patch also fixes a case there the MinorCPU creates a packet
without a valid address and size, only to later delete it.
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The Packet::get() and Packet::set() methods both have very strange
semantics. Currently, they automatically convert between the guest
system's endianness and the host system's endianness. This behavior is
usually undesired and unexpected.
This patch introduces three new method pairs to access data:
* getLE() / setLE() - Get data stored as little endian.
* getBE() / setBE() - Get data stored as big endian.
* get(ByteOrder) / set(v, ByteOrder) - Configurable endianness
For example, a little endian device that is receiving a write request
will use teh getLE() method to get the data from the packet.
The old interface will be deprecated once all existing devices have
been ported to the new interface.
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This patch removes the extraneous flags and attributes from the
request and packet, and simply leaves the new commands. The change
introduced when adding acquire/release breaks all compatibility with
existing traces, and there is really no need for any new flags and
attributes. The commands should be sufficient.
This patch fixes packet tracing (urgent), and also removes the
unnecessary complexity.
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Add support for acquire and release requests. These synchronization operations
are commonly supported by several modern instruction sets.
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This patch changes how writebacks communicate whether the line is
passed as modified or owned. Previously we relied on the
isSupplyExclusive mechanism, which was originally designed to avoid
unecessary snoops.
For normal cache requests we use the sharedAsserted mechanism to
determine if a block should be marked writeable or not, and with this
patch we transition the writebacks to also use this
mechanism. Conceptually this is cleaner and more consistent.
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Some minor fixes and removal of dead code. Changing the flags to be
enums rather than static const (to avoid any linking issues caused by
the latter). Also adding a getBlockAddr member which hopefully can
slowly finds its way into caches, snoop filters etc.
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WriteInvalidateReq ensures that a whole-line write does not incur the
cost of first doing a read exclusive, only to later overwrite the
data. This patch splits the existing WriteInvalidateReq into a
WriteLineReq, which is done locally, and an InvalidateReq that is sent
out throughout the memory system. The WriteLineReq re-uses the normal
WriteResp.
The change allows us to better express the difference between the
cache that is performing the write, and the ones that are merely
invalidating. As a consequence, we no longer have to rely on the
isTopLevel flag. Moreover, the actual memory in the system does not
see the intitial write, only the writeback. We were marking the
written line as dirty already, so there is really no need to also push
the write all the way to the memory.
The overall flow of the write-invalidate operation remains the same,
i.e. the operation is only carried out once the response for the
invalidate comes back. This patch adds the InvalidateResp for this
very reason.
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This patch adds two new read requests packets:
ReadCleanReq - For a cache to explicitly request clean data. The
response is thus exclusive or shared, but not owned or modified. The
read-only caches (see previous patch) use this request type to ensure
they do not get dirty data.
ReadSharedReq - We add this to distinguish cache read requests from
those issued by other masters, such as devices and CPUs. Thus, devices
use ReadReq, and caches use ReadCleanReq, ReadExReq, or
ReadSharedReq. For the latter, the response can be any state, shared,
exclusive, owned or even modified.
Both ReadCleanReq and ReadSharedReq re-use the normal ReadResp. The
two transactions are aligned with the emerging cache-coherent TLM
standard and the AMBA nomenclature.
With this change, the normal ReadReq should never be used by a cache,
and is reserved for the actual (non-caching) masters in the system. We
thus have a way of identifying if a request came from a cache or
not. The introduction of ReadSharedReq thus removes the need for the
current isTopLevel hack, and also allows us to stop relying on
checking the packet size to determine if the source is a cache or
not. This is fixed in follow-on patches.
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This patch adds eviction notices to the caches, to provide accurate
tracking of cache blocks in snoop filters. We add the CleanEvict
message to the memory heirarchy and use both CleanEvicts and
Writebacks with BLOCK_CACHED flags to propagate notice of clean and
dirty evictions respectively, down the memory hierarchy. Note that the
BLOCK_CACHED flag indicates whether there exist any copies of the
evicted block in the caches above the evicting cache.
The purpose of the CleanEvict message is to notify snoop filters of
silent evictions in the relevant caches. The CleanEvict message
behaves much like a Writeback. CleanEvict is a write and a request but
unlike a Writeback, CleanEvict does not have data and does not need
exclusive access to the block. The cache generates the CleanEvict
message on a fill resulting in eviction of a clean block. Before
travelling downwards CleanEvict requests generate zero-time snoop
requests to check if the same block is cached in upper levels of the
memory heirarchy. If the block exists, the cache discards the
CleanEvict message. The snoops check the tags, writeback queue and the
MSHRs of upper level caches in a manner similar to snoops generated
from HardPFReqs. Currently CleanEvicts keep travelling towards main
memory unless they encounter the block corresponding to their address
or reach main memory (since we have no well defined point of
serialisation). Main memory simply discards CleanEvict messages.
We have modified the behavior of Writebacks, such that they generate
snoops to check for the presence of blocks in upper level caches. It
is possible in our current implmentation for a lower level cache to be
writing back a block while a shared copy of the same block exists in
the upper level cache. If the snoops find the same block in upper
level caches, we set the BLOCK_CACHED flag in the Writeback message.
We have also added logic to account for interaction of other message
types with CleanEvicts waiting in the writeback queue. A simple
example is of a response arriving at a cache removing any CleanEvicts
to the same address from the cache's writeback queue.
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Snoop packets share the request pointer with the originating
packets. We need to ensure that the snoop packet destruction does not
delete the request. Snoops are used for reads, invalidations,
HardPFReqs, Writebacks and CleansEvicts. Reads, invalidations, and
HardPFReqs need a response so their snoops do not delete the
request. For Writebacks and CleanEvicts we need to check explicitly
for whethere the current packet is an express snoop, in whcih case do
not delete the request.
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This patch subsumes the PREFETCH_SNOOP_SQUASH flag with the more
generic BLOCK_CACHED flag. Future patches implementing cache eviction
messages can use the BLOCK_CACHED flag in almost the same manner as
hardware prefetches use the PREFETCH_SNOOP_SQUASH flag. The
PREFTECH_SNOOP_FLAG is set if the prefetch target is found in the tags
or the MSHRs in any state, so we are simply replacing calls to
setPrefetchSquashed() with setBlockCached(). The case of where the
prefetch target is found in the writeback MSHRs of upper level caches
continues to be covered by the MEM_INHIBIT flag.
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Refactor the way that specific MemCmd values are generated for packets.
The new approach is a little more elegant in that we assign the right
value up front, and it's also more amenable to non-heap-allocated
Packet objects.
Also replaced the code in the Minor model that was still doing it the
ad-hoc way.
This is basically a refinement of http://repo.gem5.org/gem5/rev/711eb0e64249.
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This patch changes the valid-bytes start/end to a proper byte
mask. With the changes in timing introduced in previous patches there
are more packets waiting in queues, and there are regressions using
the checker CPU failing due to non-contigous read data being found in
the various cache queues.
This patch also adds some more comments explaining what is going on,
and adds the fourth and missing case to Packet::checkFunctional.
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This patch clarifies the packet timings annotated
when going through a crossbar.
The old 'firstWordDelay' is replaced by 'headerDelay' that represents
the delay associated to the delivery of the header of the packet.
The old 'lastWordDelay' is replaced by 'payloadDelay' that represents
the delay needed to processing the payload of the packet.
For now the uses and values remain identical. However, going forward
the payloadDelay will be additive, and not include the
headerDelay. Follow-on patches will make the headerDelay capture the
pipeline latency incurred in the crossbar, whereas the payloadDelay
will capture the additional serialisation delay.
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This patch takes the final step in removing the src and dest fields in
the packet. These fields were rather confusing in that they only
remember a single multiplexing component, and pushed the
responsibility to the bridge and caches to store the fields in a
senderstate, thus effectively creating a stack. With the recent
changes to the crossbar response routing the crossbar is now
responsible without relying on the packet fields. Thus, these
variables are now unused and can be removed.
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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.
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This patch allows objects to get the src/dest of a packet even if it
is not set to a valid port id. This simplifies (ab)using the bridge as
a buffer and latency adapter in situations where the neighbouring
MemObjects are not crossbars.
The checks that were done in the packet are now shifted to the
crossbar where the fields are used to index into the port
arrays. Thus, the carrier of the information is not burdened with
checking, and the crossbar can check not only that the destination is
set, but also that the port index is within limits.
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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).
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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.
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