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115 commits

Author SHA1 Message Date
Krishnendra Nathella
cabd4768c7 cpu: Fix LLSC atomic CPU wakeup
Writes to locked memory addresses (LLSC) did not wake up the locking
CPU. This can lead to deadlocks on multi-core runs. In AtomicSimpleCPU,
recvAtomicSnoop was checking if the incoming packet was an invalidation
(isInvalidate) and only then handled a locked snoop. But, writes are
seen instead of invalidates when running without caches (fast-forward
configurations). As as simple fix, now handleLockedSnoop is also called
even if the incoming snoop packet are from writes.
2015-07-19 15:03:30 -05:00
Pau Cabre
abfb997800 cpu: fix unitialized variable which may cause assertion failure
The assert in lsq_unit_impl.hh line 963 needs pktPending to be initialized to
NULL (I got the assertion failure several times without the fix).

Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2015-12-04 17:54:03 -06:00
Hongil Yoon
fb0f9884e2 cpu, o3: consider split requests for LSQ checksnoop operations
This patch enables instructions in LSQ to track two physical addresses for
corresponding two split requests. Later, the information is used in
checksnoop() to search for/invalidate the corresponding LD instructions.

The current implementation has kept track of only the physical address that is
referenced by the first split request. Thus, for checksnoop(), the line
accessed by the second request has not been considered, causing potential
correctness issues.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2015-09-15 08:14:06 -05:00
Andreas Sandberg
48281375ee mem, cpu: Add a separate flag for strictly ordered memory
The Request::UNCACHEABLE flag currently has two different
functions. The first, and obvious, function is to prevent the memory
system from caching data in the request. The second function is to
prevent reordering and speculation in CPU models.

This changeset gives the order/speculation requirement a separate flag
(Request::STRICT_ORDER). This flag prevents CPU models from doing the
following optimizations:

    * Speculation: CPU models are not allowed to issue speculative
      loads.

    * Write combining: CPU models and caches are not allowed to merge
      writes to the same cache line.

Note: The memory system may still reorder accesses unless the
UNCACHEABLE flag is set. It is therefore expected that the
STRICT_ORDER flag is combined with the UNCACHEABLE flag to prevent
this behavior.
2015-05-05 03:22:33 -04:00
Marco Elver
9649395f85 cpu, o3: Ignored invalidate causing same-address load reordering
In case the memory subsystem sends a combined response with invalidate
(e.g.  ReadRespWithInvalidate), we cannot ignore the invalidate part
of the response.

If we were to ignore the invalidate part, under certain circumstances
this effectively leads to reordering of loads to the same address
which is not permitted under any memory consistency model implemented
in gem5.

Consider the case where a later load's address is computed before an
earlier load in program order, and is therefore sent to the memory
subsystem first. At some point the earlier load's address is computed
and in doing so correctly marks the later load as a
possibleLoadViolation. In the meantime some other node writes and
sends invalidations to all other nodes. The invalidation races with
the later load's ReadResp, and arrives before ReadResp and is
deferred.  Upon receipt of the ReadResp, the response is changed to
ReadRespWithInvalidate, and sent to the CPU. If we ignore the
invalidate part of the packet, we let the later load read the old
value of the address.  Eventually the earlier load's ReadResp arrives,
but with new data. As there was no invalidate snoop (sunk into the
ReadRespWithInvalidate), and if we did not process the invalidate of
the ReadRespWithInvalidate, we obtain a load reordering.

A similar scenario can be constructed where the earlier load's address
is computed after ReadRespWithInvalidate arrives for the younger
load. In this case hitExternalSnoop needs to be set to true on the
ReadRespWithInvalidate, so that upon knowing the address of the
earlier load, checkViolations will cause the later load to be
squashed.

Finally we must account for the case where both loads are sent to the
memory subsystem (reordered), a snoop invalidate arrives and correctly
sets the later loads fault to ReExec. However, before the CPU
processes the fault, the later load's ReadResp arrives and the
writeback discards the outstanding fault. We must add a check to
ensure that we do not skip any unprocessed faults.
2014-12-02 06:08:03 -05:00
Stephan Diestelhorst
810349a8a7 cpu: Move packet deallocation to recvTimingResp in the O3 CPU
Move the packet deallocations in the O3 CPU so that the completeDataAccess
deals only with the LSQ specific parts and the generic recvTimingResp frees the
packet in all other cases.
2014-12-02 06:07:58 -05:00
Andreas Hansson
a2d246b6b8 arch: Use shared_ptr for all Faults
This patch takes quite a large step in transitioning from the ad-hoc
RefCountingPtr to the c++11 shared_ptr by adopting its use for all
Faults. There are no changes in behaviour, and the code modifications
are mostly just replacing "new" with "make_shared".
2014-10-16 05:49:51 -04:00
Andreas Hansson
0fa128bbd0 base: Clean up redundant string functions and use C++11
This patch does a bit of housekeeping on the string helper functions
and relies on the C++11 standard library where possible. It also does
away with our custom string hash as an implementation is already part
of the standard library.
2014-09-20 17:17:49 -04:00
Curtis Dunham
e3b19cb294 mem: Refactor assignment of Packet types
Put the packet type swizzling (that is currently done in a lot of places)
into a refineCommand() member function.
2014-05-13 12:20:48 -05:00
Mitch Hayenga
4f13f676aa cpu: Fix cache blocked load behavior in o3 cpu
This patch fixes the load blocked/replay mechanism in the o3 cpu.  Rather than
flushing the entire pipeline, this patch replays loads once the cache becomes
unblocked.

Additionally, deferred memory instructions (loads which had conflicting stores),
when replayed would not respect the number of functional units (only respected
issue width).  This patch also corrects that.

Improvements over 20% have been observed on a microbenchmark designed to
exercise this behavior.
2014-09-03 07:42:39 -04:00
Mitch Hayenga
976f27487b cpu: Change writeback modeling for outstanding instructions
As highlighed on the mailing list gem5's writeback modeling can impact
performance.  This patch removes the limitation on maximum outstanding issued
instructions, however the number that can writeback in a single cycle is still
respected in instToCommit().
2014-09-03 07:42:33 -04:00
Binh Pham
0782d92286 o3: split load & store queue full cases in rename
Check for free entries in Load Queue and Store Queue separately to
avoid cases when load cannot be renamed due to full Store Queue and
vice versa.

This work was done while Binh was an intern at AMD Research.
2014-06-21 10:26:43 -07:00
Steve Reinhardt
0be64ffe2f style: eliminate equality tests with true and false
Using '== true' in a boolean expression is totally redundant,
and using '== false' is pretty verbose (and arguably less
readable in most cases) compared to '!'.

It's somewhat of a pet peeve, perhaps, but I had some time
waiting for some tests to run and decided to clean these up.

Unfortunately, SLICC appears not to have the '!' operator,
so I had to leave the '== false' tests in the SLICC code.
2014-05-31 18:00:23 -07:00
Mitch Hayenga
e4086878f6 cpu: Fix case where o3 lsq could print out uninitialized data
In the O3 LSQ, data read/written is printed out in DPRINTFs.  However,
the data field is treated as a character string with a null terminated.
However the data field is not encoded this way.  This patch removes
that possibility by removing the data part of the print.
2014-04-01 14:22:06 -05:00
Marco Elver
b884fcf412 cpu: o3: lsq: Fix TSO implementation
This patch fixes violation of TSO in the O3CPU, as all loads must be
ordered with all other loads. In the LQ, if a snoop is observed, all
subsequent loads need to be squashed if the system is TSO.

Prior to this patch, the following case could be violated:

 P0         | P1          ;
 MOV [x],mail=/usr/spool/mail/nilay | MOV EAX,[y] ;
 MOV [y],mail=/usr/spool/mail/nilay | MOV EBX,[x] ;

exists (1:EAX=1 /\ 1:EBX=0) [is a violation]

The problem was found using litmus [http://diy.inria.fr].

Committed by: Nilay Vaish <nilay@cs.wisc.edu
2014-03-25 13:15:04 -05:00
Ali Saidi
90b1775a8f cpu: Add support for instructions that zero cache lines. 2014-01-24 15:29:30 -06:00
Ali Saidi
6bed6e0352 cpu: Add CPU support for generatig wake up events when LLSC adresses are snooped.
This patch add support for generating wake-up events in the CPU when an address
that is currently in the exclusive state is hit by a snoop. This mechanism is required
for ARMv8 multi-processor support.
2014-01-24 15:29:30 -06:00
Matt Horsnell
739c6df94e base: add support for probe points and common probes
The probe patch is motivated by the desire to move analytical and trace code
away from functional code. This is achieved by the probe interface which is
essentially a glorified observer model.

What this means to users:
* add a probe point and a "notify" call at the source of an "event"
* add an isolated module, that is being used to carry out *your* analysis (e.g. generate a trace)
* register that module as a probe listener
Note: an example is given for reference in src/cpu/o3/simple_trace.[hh|cc] and src/cpu/SimpleTrace.py

What is happening under the hood:
* every SimObject maintains has a ProbeManager.
* during initialization (src/python/m5/simulate.py) first regProbePoints and
  the regProbeListeners is called on each SimObject.  this hooks up the probe
  point notify calls with the listeners.

FAQs:
Why did you develop probe points:
* to remove trace, stats gathering, analytical code out of the functional code.
* the belief that probes could be generically useful.

What is a probe point:
* a probe point is used to notify upon a given event (e.g. cpu commits an instruction)

What is a probe listener:
* a class that handles whatever the user wishes to do when they are notified
  about an event.

What can be passed on notify:
* probe points are templates, and so the user can generate probes that pass any
  type of argument (by const reference) to a listener.

What relationships can be generated (1:1, 1:N, N:M etc):
* there isn't a restriction. You can hook probe points and listeners up in a
  1:1, 1:N, N:M relationship. They become useful when a number of modules
  listen to the same probe points. The idea being that you can add a small
  number of probes into the source code and develop a larger number of useful
  analysis modules that use information passed by the probes.

Can you give examples:
* adding a probe point to the cpu's commit method allows you to build a trace
  module (outputting assembler), you could re-use this to gather instruction
  distribution (arithmetic, load/store, conditional, control flow) stats.

Why is the probe interface currently restricted to passing a const reference:
* the desire, initially at least, is to allow an interface to observe
  functionality, but not to change functionality.
* of course this can be subverted by const-casting.

What is the performance impact of adding probes:
* when nothing is actively listening to the probes they should have a
  relatively minor impact. Profiling has suggested even with a large number of
  probes (60) the impact of them (when not active) is very minimal (<1%).
2014-01-24 15:29:30 -06:00
Matt Horsnell
ca89eba79e mem: track per-request latencies and access depths in the cache hierarchy
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.
2014-01-24 15:29:30 -06:00
Matt Horsnell
6decd70bfb cpu: add consistent guarding to *_impl.hh files. 2013-10-17 10:20:45 -05:00
Faissal Sleiman
e516531bd0 cpu: Put in assertions to check for maximum supported LQ/SQ size
LSQSenderState represents the LQ/SQ index using uint8_t, which supports up to
 256 entries (including the sentinel entry). Sending packets to memory with a
higher index than 255 truncates the index, such that the response matches the
wrong entry. For instance, this can result in a deadlock if a store completion
does not clear the head entry.
2013-10-17 10:20:45 -05:00
Andreas Hansson
d4273cc9a6 mem: Set the cache line size on a system level
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.
2013-07-18 08:31:16 -04:00
Matt Horsnell
e88e7d88b9 o3: fix tick used for renaming and issue with range selection
Fixes the tick used from rename:
- previously this gathered the tick on leaving rename which was always 1 less
  than the dispatch. This conflated the decode ticks when back pressure built
  in the pipeline.
- now picks up tick on entry.

Added --store_completions flag:
- will additionally display the store completion tail in the viewer.
- this highlights periods when large numbers of stores are outstanding (>16 LSQ
  blocking)

Allows selection by tick range (previously this caused an infinite loop)
2013-02-15 17:40:09 -05:00
Andreas Sandberg
1814a85a05 cpu: Rewrite O3 draining to avoid stopping in microcode
Previously, the O3 CPU could stop in the middle of a microcode
sequence. This patch makes sure that the pipeline stops when it has
committed a normal instruction or exited from a microcode
sequence. Additionally, it makes sure that the pipeline has no
instructions in flight when it is drained, which should make draining
more robust.

Draining is controlled in the commit stage, which checks if the next
PC after a committed instruction is in microcode. If this isn't the
case, it requests a squash of all instructions after that the
instruction that just committed and immediately signals a drain stall
to the fetch stage. The CPU then continues to execute until the
pipeline and all associated buffers are empty.
2013-01-07 13:05:46 -05:00
Andreas Sandberg
fca4fea769 cpu: Fix O3 LSQ debug dumping constness and formatting 2013-01-07 13:05:46 -05:00
Ali Saidi
69d419f313 o3: Fix issue with LLSC ordering and speculation
This patch unlocks the cpu-local monitor when the CPU sees a snoop to a locked
address. Previously we relied on the cache to handle the locking for us, however
some users on the gem5 mailing list reported a case where the cpu speculatively
executes a ll operation after a pending sc operation in the pipeline and that
makes the cache monitor valid. This should handle that case by invaliding the
local monitor.
2013-01-07 13:05:33 -05:00
Nathanael Premillieu
eb899407c5 o3 cpu: remove some unused buggy functions in the lsq
Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2012-12-06 04:36:51 -06:00
Andreas Hansson
c60db56741 Packet: Remove NACKs from packet and its use in endpoints
This patch removes the NACK frrom the packet as there is no longer any
module in the system that issues them (the bridge was the only one and
the previous patch removes that).

The handling of NACKs was mostly avoided throughout the code base, by
using e.g. panic or assert false, but in a few locations the NACKs
were actually dealt with (although NACKs never occured in any of the
regressions). Most notably, the DMA port will now never receive a NACK
and the backoff time is thus never changed. As a consequence, the
entire backoff mechanism (similar to a PCI bus) is now removed and the
DMA port entirely relies on the bus performing the arbitration and
issuing a retry when appropriate. This is more in line with e.g. PCIe.

Surprisingly, this patch has no impact on any of the regressions. As
mentioned in the patch that removes the NACK from the bridge, a
follow-up patch should change the request and response buffer size for
at least one regression to also verify that the system behaves as
expected when the bridge fills up.
2012-08-22 11:39:59 -04:00
Ali Saidi
6df196b71e O3: Clean up the O3 structures and try to pack them a bit better.
DynInst is extremely large the hope is that this re-organization will put the
most used members close to each other.
2012-06-05 01:23:09 -04:00
Andreas Hansson
3fea59e162 MEM: Separate requests and responses for timing accesses
This patch moves send/recvTiming and send/recvTimingSnoop from the
Port base class to the MasterPort and SlavePort, and also splits them
into separate member functions for requests and responses:
send/recvTimingReq, send/recvTimingResp, and send/recvTimingSnoopReq,
send/recvTimingSnoopResp. A master port sends requests and receives
responses, and also receives snoop requests and sends snoop
responses. A slave port has the reciprocal behaviour as it receives
requests and sends responses, and sends snoop requests and receives
snoop responses.

For all MemObjects that have only master ports or slave ports (but not
both), e.g. a CPU, or a PIO device, this patch merely adds more
clarity to what kind of access is taking place. For example, a CPU
port used to call sendTiming, and will now call
sendTimingReq. Similarly, a response previously came back through
recvTiming, which is now recvTimingResp. For the modules that have
both master and slave ports, e.g. the bus, the behaviour was
previously relying on branches based on pkt->isRequest(), and this is
now replaced with a direct call to the apprioriate member function
depending on the type of access. Please note that send/recvRetry is
still shared by all the timing accessors and remains in the Port base
class for now (to maintain the current bus functionality and avoid
changing the statistics of all regressions).

The packet queue is split into a MasterPort and SlavePort version to
facilitate the use of the new timing accessors. All uses of the
PacketQueue are updated accordingly.

With this patch, the type of packet (request or response) is now well
defined for each type of access, and asserts on pkt->isRequest() and
pkt->isResponse() are now moved to the appropriate send member
functions. It is also worth noting that sendTimingSnoopReq no longer
returns a boolean, as the semantics do not alow snoop requests to be
rejected or stalled. All these assumptions are now excplicitly part of
the port interface itself.
2012-05-01 13:40:42 -04:00
Andreas Hansson
750f33a901 MEM: Remove the Broadcast destination from the packet
This patch simplifies the packet by removing the broadcast flag and
instead more firmly relying on (and enforcing) the semantics of
transactions in the classic memory system, i.e. request packets are
routed from a master to a slave based on the address, and when they
are created they have neither a valid source, nor destination. On
their way to the slave, the request packet is updated with a source
field for all modules that multiplex packets from multiple master
(e.g. a bus). When a request packet is turned into a response packet
(at the final slave), it moves the potentially populated source field
to the destination field, and the response packet is routed through
any multiplexing components back to the master based on the
destination field.

Modules that connect multiplexing components, such as caches and
bridges store any existing source and destination field in the sender
state as a stack (just as before).

The packet constructor is simplified in that there is no longer a need
to pass the Packet::Broadcast as the destination (this was always the
case for the classic memory system). In the case of Ruby, rather than
using the parameter to the constructor we now rely on setDest, as
there is already another three-argument constructor in the packet
class.

In many places where the packet information was printed as part of
DPRINTFs, request packets would be printed with a numeric "dest" that
would always be -1 (Broadcast) and that field is now removed from the
printing.
2012-04-14 05:45:55 -04:00
William Wang
f9d403a7b9 MEM: Introduce the master/slave port sub-classes in C++
This patch introduces the notion of a master and slave port in the C++
code, thus bringing the previous classification from the Python
classes into the corresponding simulation objects and memory objects.

The patch enables us to classify behaviours into the two bins and add
assumptions and enfore compliance, also simplifying the two
interfaces. As a starting point, isSnooping is confined to a master
port, and getAddrRanges to slave ports. More of these specilisations
are to come in later patches.

The getPort function is not getMasterPort and getSlavePort, and
returns a port reference rather than a pointer as NULL would never be
a valid return value. The default implementation of these two
functions is placed in MemObject, and calls fatal.

The one drawback with this specific patch is that it requires some
code duplication, e.g. QueuedPort becomes QueuedMasterPort and
QueuedSlavePort, and BusPort becomes BusMasterPort and BusSlavePort
(avoiding multiple inheritance). With the later introduction of the
port interfaces, moving the functionality outside the port itself, a
lot of the duplicated code will disappear again.
2012-03-30 09:40:11 -04:00
Geoffrey Blake
043709fdfa CheckerCPU: Make CheckerCPU runtime selectable instead of compile selectable
Enables the CheckerCPU to be selected at runtime with the --checker option
from the configs/example/fs.py and configs/example/se.py configuration
files.  Also merges with the SE/FS changes.
2012-03-09 09:59:27 -05:00
Geoffrey Blake
af6aaf2581 CheckerCPU: Re-factor CheckerCPU to be compatible with current gem5
Brings the CheckerCPU back to life to allow FS and SE checking of the
O3CPU.  These changes have only been tested with the ARM ISA.  Other
ISAs potentially require modification.
2012-01-31 07:46:03 -08:00
Nilay Vaish
5c2fc35e02 O3 CPU LSQ: Implement TSO
This patch makes O3's LSQ maintain total order between stores. Essentially
only the store at the head of the store buffer is allowed to be in flight.
Only after that store completes, the next store is issued to the memory
system. By default, the x86 architecture will have TSO.
2012-01-28 19:09:04 -06:00
Gabe Black
4fcf8e9959 O3: Tidy up some DPRINTFs in the LSQ. 2011-09-27 00:25:26 -07:00
Gabe Black
44ed4849d4 Faults: Replace calls to genMachineCheckFault with M5PanicFault. 2011-09-27 00:24:43 -07:00
Nilay Vaish
56bddab189 LSQ: Moved a couple of lines to enable O3 + Ruby
This patch makes O3 CPU work along with the Ruby memory model. Ruby
overwrites the senderState pointer with another pointer. The pointer
is restored only when Ruby gets done with the packet. LSQ makes use of
senderState just after sendTiming() returns. But the dynamic_cast returns
a NULL pointer since Ruby's senderState pointer is from a different class.
Storing the senderState pointer before calling sendTiming() does away with
the problem.
2011-09-26 12:18:32 -05:00
Steve Reinhardt
84f0a1bd91 event: minor cleanup
Initialize flags via the Event constructor instead of calling
setFlags() in the body of the derived class's constructor.  I
forget exactly why, but this made life easier when implementing
multi-queue support.

Also rename Event::getFlags() to isFlagSet() to better match
common usage, and get rid of some unused Event methods.
2011-09-22 18:59:55 -07:00
Ali Saidi
649c239cee LSQ: Only trigger a memory violation with a load/load if the value changes.
Only create a memory ordering violation when the value could have changed
between two subsequent loads, instead of just when loads go out-of-order
to the same address. While not very common in the case of Alpha, with
an architecture with a hardware table walker this can happen reasonably
frequently beacuse a translation will miss and start a table walk and
before the CPU re-schedules the faulting instruction another one will
pass it to the same address (or cache block depending on the dendency
checking).

This patch has been tested with a couple of self-checking hand crafted
programs to stress ordering between two cores.

The performance improvement on SPEC benchmarks can be substantial (2-10%).
2011-09-13 12:58:08 -04:00
Gabe Black
206c2e9a0e O3: Implement memory mapped IPRs for O3. 2011-07-31 19:21:17 -07:00
Ali Saidi
09a2be0c39 O3: Fix a small corner case with the lsq hazard detection logic. 2011-05-04 20:38:26 -05:00
Nathan Binkert
6e9143d36d stats: one more name violation 2011-04-20 19:07:45 -07:00
Nathan Binkert
eddac53ff6 trace: reimplement the DTRACE function so it doesn't use a vector
At the same time, rename the trace flags to debug flags since they
have broader usage than simply tracing.  This means that
--trace-flags is now --debug-flags and --trace-help is now --debug-help
2011-04-15 10:44:32 -07:00
Nathan Binkert
39a055645f includes: sort all includes 2011-04-15 10:44:06 -07:00
Ali Saidi
7dde557fdc O3: Tighten memory order violation checking to 16 bytes.
The comment in the code suggests that the checking granularity should be 16
bytes, however in reality the shift by 8 is 256 bytes which seems much
larger than required.
2011-04-04 11:42:23 -05:00
Ali Saidi
2f40b3b8ae O3: Fix unaligned stores when cache blocked
Without this change the a store can be issued to the cache multiple times.
If this case occurs when the l1 cache is out of mshrs (and thus blocked)
the processor will never make forward progress because each cycle it will
send a single request using the recently freed mshr and not completing the
multipart store. This will continue forever.
2011-03-17 19:20:19 -05:00
Giacomo Gabrielli
e2507407b1 O3: Enhance data address translation by supporting hardware page table walkers.
Some ISAs (like ARM) relies on hardware page table walkers.  For those ISAs,
when a TLB miss occurs, initiateTranslation() can return with NoFault but with
the translation unfinished.

Instructions experiencing a delayed translation due to a hardware page table
walk are deferred until the translation completes and kept into the IQ.  In
order to keep track of them, the IQ has been augmented with a queue of the
outstanding delayed memory instructions.  When their translation completes,
instructions are re-executed (only their initiateAccess() was already
executed; their DTB translation is now skipped).  The IEW stage has been
modified to support such a 2-pass execution.
2011-02-11 18:29:35 -06:00
Matt Horsnell
11bef2ab38 O3: Fix corner cases where multiple squashes/fetch redirects overwrite timebuf. 2011-01-18 16:30:05 -06:00
Ali Saidi
0f9a3671b6 ARM: Add support for moving predicated false dest operands from sources. 2011-01-18 16:30:02 -06:00