This patch adds a frontend and backend static latency to the DRAM
controller by delaying the responses. Two parameters expressing the
frontend and backend contributions in absolute time are added to the
controller, and the appropriate latency is added to the responses when
adding them to the (infinite) queued port for sending.
For writes and reads that hit in the write buffer, only the frontend
latency is added. For reads that are serviced by the DRAM, the static
latency is the sum of the pipeline latencies of the entire frontend,
backend and PHY. The default values are chosen based on having roughly
10 pipeline stages in total at 500 MHz.
In the future, it would be sensible to make the controller use its
clock and convert these latencies (and a few of the DRAM timings) to
cycles.
This patch does some minor tidying up of the MSHR and MSHRQueue. The
clean up started as part of some ad-hoc tracing and debugging, but
seems worthwhile enough to go in as a separate patch.
The highlights of the changes are reduced scoping (private) members
where possible, avoiding redundant new/delete, and constructor
initialisation to please static code analyzers.
This patch introduces a mirrored internal snoop port to facilitate
easy addition of flow control for the snoop responses that are turned
into normal responses on their return. To perform this, the slave
ports of the coherent bus are wrapped in internal master ports that
are passed as the source ports to the response layer in question.
As a result of this patch, there is more contention for the response
resources, and as such system performance will decrease slightly.
A consequence of the mirrored internal port is that the port the bus
tells to retry (the internal one) and the port actually retrying (the
mirrored) one are not the same. Thus, the existing check in tryTiming
is not longer correct. In fact, the test is redundant as the layer is
only in the retry state while calling sendRetry on the waiting port,
and if the latter does not immediately call the bus then the retry
state is left. Consequently the check is removed.
This patch makes the buses multi layered, and effectively creates a
crossbar structure with distributed contention ports at the
destination ports. Before this patch, a bus could have a single
request, response and snoop response in flight at any time, and with
these changes there can be as many requests as connected slaves (bus
master ports), and as many responses as connected masters (bus slave
ports).
Together with address interleaving, this patch enables us to create
high-throughput memory interconnects, e.g. 50+ GByte/s.
This patch makes the flow control and state updates of the coherent
bus more clear by separating the two cases, i.e. forward as a snoop
response, or turn it into a normal response.
With this change it is also more clear what resources are being
occupied, and that we effectively bypass the busy check for the second
case. As a result of the change in resource usage some stats change.
This patch does some minor housekeeping on the bus code, removing
redundant code, and moving the extraction of the destination id to the
top of the functions using it.
This patch adds a basic set of stats which are hard to impossible to
implement using only communication monitors, and are needed for
insight such as bus utilization, transactions through the bus etc.
Stats added include throughput and transaction distribution, and also
a two-dimensional vector capturing how many packets and how much data
is exchanged between the masters and slaves connected to the bus.
This patch changes the set used to track outstanding requests to an
unordered set (part of C++11 STL). There is no need to maintain the
order, and hopefully there might even be a small performance benefit.
This patch adds a typical (leaning towards fast) LPDDR3 configuration
based on publically available data. As expected, it looks very similar
to the LPDDR2-S4 configuration, only with a slightly lower burst time.
This patch adapts the existing LPDDR2 configuration to make use of the
multi-channel functionality. Thus, to get a x64 interface two
controllers should be instantiated using the makeMultiChannel method.
The page size and ranks are also adapted to better suit with a typical
LPDDR2 part.
This patch removes the explicit memset as it is redundant and causes
the simulator to touch the entire space, forcing the host system to
allocate the pages.
Anonymous pages are mapped on the first access, and the page-fault
handler is responsible for zeroing them. Thus, the pages are still
zeroed, but we avoid touching the entire allocated space which enables
us to use much larger memory sizes as long as not all the memory is
actually used.
This patch changes the way cache statistics are collected in ruby.
As of now, there is separate entity called CacheProfiler which holds
statistical variables for caches. The CacheMemory class defines different
functions for accessing the CacheProfiler. These functions are then invoked
in the .sm files. I find this approach opaque and prone to error. Secondly,
we probably should not be paying the cost of a function call for recording
statistics.
Instead, this patch allows for accessing statistical variables in the
.sm files. The collection would become transparent. Secondly, it would happen
in place, so no function calls. The patch also removes the CacheProfiler class.
--HG--
rename : src/mem/slicc/ast/InfixOperatorExprAST.py => src/mem/slicc/ast/OperatorExprAST.py
The existing implementation can read uninitialized data or stale information
from the cached PageTable entries.
1) Add a valid bit for the cache entries. Simply using zero for the virtual
address to signify invalid entries is not sufficient. Speculative, wrong-path
accesses frequently access page zero. The current implementation would return
a uninitialized TLB entry when address zero was accessed and the PageTable
cache entry was invalid.
2) When unmapping/mapping/remaping a page, invalidate the corresponding
PageTable cache entry if one already exists.
Due to recent changes to clocking system in Ruby and the way Ruby restores
state from a checkpoint, garnet was failing to run from a checkpointed state.
The problem is that Ruby resets the time to zero while warming up the caches.
If any component records a local copy of the time (read calls curCycle())
before the simulation has started, then that component will not operate until
that time is reached. In the context of this particular patch, the Garnet
Network class calls curCycle() at multiple places. Any non-operational
component can block in requests in the memory system, which the system
interprets as a deadlock. This patch makes changes so that Garnet can
successfully run from checkpointed state.
It adds a globally visible time at which the actual execution started. This
time is initialized in RubySystem::startup() function. This variable is only
meant for components with in Ruby. This replaces the private variable that
was maintained within Garnet since it is not possible to figure out the
correct time when the value of this variable can be set.
The patch also does away with all cases where curCycle() is called with in
some Ruby component before the system has actually started executing. This
is required due to the quirky manner in which ruby restores from a checkpoint.
This patch adds an address mapping scheme where the channel
interleaving takes place on a cache line granularity. It is similar to
the existing RaBaChCo that interleaves on a DRAM page, but should give
higher performance when there is less locality in the address
stream.
This patch changes the slightly ambigious names used for the address
mapping scheme to be more descriptive, and actually spell out what
they do. With this patch we also open up for adding more flavours of
open- and close-type mappings, i.e. interleaving across channels with
the open map.
This patch adds a WideIO 200 MHz configuration that can be used as a
baseline to compare with DDRx and LPDDRx. Note that it is a single
channel and that it should be replicated 4 times. It is based on
publically available information and attempts to capture an envisioned
8 Gbit single-die part (i.e. without TSVs).
This patch provides useful printouts throughut the memory system. This
includes pretty-printed cache tags and function call messages
(call-stack like).
This patch changes the SimpleTimingPort and RubyPort to panic on
inhibited requests as this should never happen in either of the
cases. The SimpleTimingPort is only used for the I/O devices PIO port
and the DMA devices config port and should thus never see an inhibited
request. Similarly, the SimpleTimingPort is also used for the
MessagePort in x86, and there should also not be any cases where the
port sees an inhibited request.
Previously, nextCycle() could return the *current* cycle if the current tick was
already aligned with the clock edge. This behavior is not only confusing (not
quite what the function name implies), but also caused problems in the
drainResume() function. When exiting/re-entering the sim loop (e.g., to take
checkpoints), the CPUs will drain and resume. Due to the previous behavior of
nextCycle(), the CPU tick events were being rescheduled in the same ticks that
were already processed before draining. This caused divergence from runs that
did not exit/re-entered the sim loop. (Initially a cycle difference, but a
significant impact later on.)
This patch separates out the two behaviors (nextCycle() and clockEdge()),
uses nextCycle() in drainResume, and uses clockEdge() everywhere else.
Nothing (other than name) should change except for the drainResume timing.
When using the o3 or inorder CPUs with many Ruby protocols, the caches may
need to forward invalidations to the CPUs. The RubyPort was instantiating a
packet to be sent to the CPUs to signal the eviction, but the packets were
not being freed by the CPUs. Consistent with the classic memory model, stack
allocate the packet and heap allocate the request so on
ruby_eviction_callback() completion, the packet deconstructor is called, and
deletes the request (*Note: stack allocating the request causes double
deletion, since it will be deleted in the packet destructor). This results in
the least memory allocations without memory errors.
When warming up caches in Ruby, the CacheRecorder sends fetch requests into
Ruby Sequencers with packet types that require responses. Since responses are
never generated for these CacheRecorder requests, the requests are not deleted
in the packet destructor called from the Ruby hit callback. Free the request.
This allows you to have (i.e.) an L2 cache that is not named "L2Cache"
but is still a GenericMachineType_L2Cache. This is particularly
helpful if the protocol has multiple L2 controllers.
When Ruby stats are printed for events and transitions, they include stats
for all of the controllers of the same type, but they are not necessarily
printed in order of the controller ID "version", because of the way the
profilers were added to the profiler vector. This patch fixes the push order
problem so that the stats are printed in ascending order 0->(# controllers),
so statistics parsers may correctly assume the controller to which the stats
belong.
When connecting message buffers between Ruby controllers, it is
easy to mistakenly connect multiple controllers to the same message
buffer. This patch prints a more descriptive fatal message than the
previous assert statement in order to facilitate easier debugging.
The cache trace variables are array allocated uint8_t* in the RubySystem and
the Ruby CacheRecorder, but the code used delete to free the memory, resulting
in Valgrind memory errors. Change these deletes to delete [] to get rid of the
errors.
Fixes a latency calculation bug for accesses during a cache line fill.
Under a cache miss, before the line is filled, accesses to the cache are
associated with a MSHR and marked as targets. Once the line fill completes,
MSHR target packets pay an additional latency of
"responseLatency + busSerializationLatency". However, the "whenReady"
field of the cache line is only set to an additional delay of
"busSerializationLatency". This lacks the responseLatency component of
the fill. It is possible for accesses that occur on the cycle of
(or briefly after) the line fill to respond without properly paying the
responseLatency. This also creates the situation where two accesses to the
same address may be serviced in an order opposite of how they were received
by the cache. For stores to the same address, this means that although the
cache performs the stores in the order they were received, acknowledgements
may be sent in a different order.
Adding the responseLatency component to the whenReady field preserves the
penalty that should be paid and prevents these ordering issues.
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
This patch solves the corner case scenario where the sendRetryEvent could be
scheduled twice, when an io device stresses the IOcache in the system. This
should not be possible in the cache system.
This patch splits the retryList into a list of ports that are waiting
for the bus itself to become available, and a map that tracks the
ports where forwarding failed due to a peer not accepting the
packet. Thus, when a retry reaches the bus, it can be sent to the
appropriate port that initiated that transaction.
As a consequence of this patch, only ports that are really ready to go
will get a retry, thus reducing the amount of redundant failed
attempts. This patch also makes it easier to reason about the order of
servicing requests as the ports waiting for the bus are now clearly
FIFO and much easier to change if desired.
This patch introduces a variable to keep track of the retrying port
instead of relying on it being the front of the retryList.
Besides the improvement in readability, this patch is a step towards
separating out the two cases where a port is waiting for the bus to be
free, and where the forwarding did not succeed and the bus is waiting
for a retry to pass on to the original initiator of the transaction.
The changes made are currently such that the regressions are not
affected. This is ensured by always prioritizing the currently
retrying port and putting it back at the front of the retry list.
This patch adds an optional flags field to the packet trace to encode
the request flags that contain information about whether the request
is (un)cacheable, instruction fetch, preftech etc.
A recent set of patches added support for multiple clock domains to ruby.
I had made some errors while writing those patches. The sender was using
the receiver side clock while enqueuing a message in the buffer. Those
errors became visible while creating (or restoring from) checkpoints. The
errors also become visible when a multi eventq scenario occurs.
The message buffer node used to keep time in terms of Cycles. Since the
sender and the receiver can have different clock periods, storing node
time in cycles requires some conversion. Instead store the time directly
in Ticks.
A set of patches was recently committed to allow multiple clock domains
in ruby. In those patches, I had inadvertently made an incorrect use of
the clocks. Suppose object A needs to schedule an event on object B. It
was possible that A accesses B's clock to schedule the event. This is not
possible in actual system. Hence, changes are being to the Consumer class
so as to avoid such happenings. Note that in a multi eventq simulation,
this can possibly lead to an incorrect simulation.
There are two functions in the Consumer class that are used for scheduling
events. The first function takes in the relative delay over the current time
as the argument and adds the current time to it for scheduling the event.
The second function takes in the absolute time (in ticks) for scheduling the
event. The first function is now being moved to protected section of the
class so that only objects of the derived classes can use it. All other
objects will have to specify absolute time while scheduling an event
for some consumer.
The histogram for tracking outstanding counts per cycle is maintained
in the profiler. For a parallel implementation of the memory system, we
need that this histogram is maintained locally. Hence it will now be
kept in the sequencer itself. The resulting histograms will be merged
when the stats are printed.
These functions are currently implemented in one of the files related to Slicc.
Since these are purely C++ functions, they are better suited to be in the base
class.
