config: Add options to take/resume from SimPoint checkpoints

More documentation at http://gem5.org/Simpoints

Steps to profile, generate, and use SimPoints with gem5:

1. To profile workload and generate SimPoint BBV file, use the
following option:

--simpoint-profile --simpoint-interval <interval length>

Requires single Atomic CPU and fastmem.
<interval length> is in number of instructions.

2. Generate SimPoint analysis using SimPoint 3.2 from UCSD.
(SimPoint 3.2 not included with this flow.)

3. To take gem5 checkpoints based on SimPoint analysis, use the
following option:

--take-simpoint-checkpoint=<simpoint file path>,<weight file
path>,<interval length>,<warmup length>

<simpoint file> and <weight file> is generated by SimPoint analysis
tool from UCSD. SimPoint 3.2 format expected. <interval length> and
<warmup length> are in number of instructions.

4. To resume from gem5 SimPoint checkpoints, use the following option:

--restore-simpoint-checkpoint -r <N> --checkpoint-dir <simpoint
checkpoint path>

<N> is (SimPoint index + 1). E.g., "-r 1" will resume from SimPoint
#0.
arm: Add support for filtering in the PMU

This patch adds support for filtering events in the PMU. In order to
do so, it updates the ISADevice base class to forward an ISA pointer
to ISA devices. This enables such devices to access the MiscReg file
to determine the current execution level.
arm: Clean up and document decoder API

This changeset adds more documentation to the ArmISA::Decoder class
and restructures it slightly to make API groups more obvious.
arm: Raise an alignment fault if a PC has illegal alignment

We currently don't handle unaligned PCs correctly. There is one check
for unaligned PCs in the TLB when running in aarch64 mode, but this
check does not cover cases where the CPU does not do a TLB lookup when
decoding an instruction (e.g., a branch stays within the same cache
line). Additionally, the Decoder class sometimes throws an assertion
for unaligned PCs which breaks speculation.

This changeset introduces a decoder fault bit field in the ExtMachInst
structure. This field can be used to signal a decoder failure. If set,
the decoder generates an internal gem5fault instruction instead of a
normal instruction. This instruction in turns either panics (fault
type PANIC), returns an PCAlignmentFault (fault type UNALIGNED,
aarch64) or PrefetchAbort (fault type UNALIGNED, aarch32).

The patch causes minor changes to the realview64 regressions, and a
stats bump will follow.
mem: Add MemChecker and MemCheckerMonitor

This patch adds the MemChecker and MemCheckerMonitor classes. While
MemChecker can be integrated anywhere in the system and is independent,
the most convenient usage is through the MemCheckerMonitor -- this
however, puts limitations on where the MemChecker is able to observe
read/write transactions.
config: Add --memchecker option

This patch adds the --memchecker option, to denote that a MemChecker
should be instantiated for the system. The exact usage of the MemChecker
depends on the system configuration.

For now CacheConfig.py makes use of the option, adding MemCheckerMonitor
instances between CPUs and D-Caches.

Note, however, that currently this only provides limited checking on a
running system; other parts of the system, such as I/O devices are not
monitored, and may cause warnings to be issued by the monitor.
mem: Add a stack distance calculator

This patch adds a stand-alone stack distance calculator. The stack
distance calculator is a passive SimObject that observes the addresses
passed to it. It calculates stack distances (LRU Distances) of
incoming addresses based on the partial sum hierarchy tree algorithm
described by Alamasi et al. http://doi.acm.org/10.1145/773039.773043.

For each transaction a hashtable look-up is performed. At every
non-unique transaction the tree is traversed from the leaf at the
returned index to the root, the old node is deleted from the tree, and
the sums (to the right) are collected and decremented. The collected
sum represets the stack distance of the found node. At every unique
transaction the stack distance is returned as
numeric_limits<uint64>::max().

In addition to the basic stack distance calculation, a feature to mark
an old node in the tree is added. This is useful if it is required to
see the reuse pattern. For example, Writebacks to the lower level
(e.g. membus from L2), can be marked instead of being removed from the
stack (isMarked flag of Node set to True). And then later if this same
address is accessed (by L1), the value of the isMarked flag would be
True. This gives some insight on how the Writeback policy of the
lower level affect the read/write accesses in an application.

Debugging is enabled by setting the verify flag to true. Debugging is
implemented using a dummy stack that behaves in a naive way, using STL
vectors. Note that this has a large impact on run time.
mem: Add stack distance statistics to the CommMonitor

This patch adds the stack distance calculator to the CommMonitor. The
stats are disabled by default.
tests: Add a regression for the stack distance calculator

Re-use the existing traffic generator regression, and enable the stack
distance calculation in the comm monitor, along with the verification
stack.

The traffic generator config is also tuned to not increase the
run-time too much (and actually have some address re-use).
mem: Fix a bug in the DRAM controller arbitration

Fix a minor issue that affects multi-rank systems.
mem: Add rank-wise refresh to the DRAM controller

This patch adds rank-wise refresh to the controller, as opposed to the
channel-wide refresh currently in place. In essence each rank can be
refreshed independently, and for this to be possible the controller
is extended with a state machine per rank.

Without this patch the data bus is always idle during a refresh, as
all the ranks are refreshing at the same time. With the rank-wise
refresh it is possible to use one rank while another one is
refreshing, and thus the data bus can be kept busy.

The patch introduces a Rank class to encapsulate the state per rank,
and also shifts all the relevant banks, activation tracking etc to the
rank. The arbitration is also updated to consider the state of the rank.
mem: Ensure DRAM controller is idle when in atomic mode

This patch addresses an issue seen with the KVM CPU where the refresh
events scheduled by the DRAM controller forces the simulator to switch
out of the KVM mode, thus killing performance.

The current patch works around the fact that we currently have no
proper API to inform a SimObject of the mode switches. Instead we rely
on drainResume being called after any switch, and cache the previous
mode locally to be able to decide on appropriate actions.

The switcheroo regression require a minor stats bump as a result.
config: Expose the DRAM ranks as a command-line option

This patch gives the user direct influence over the number of DRAM
ranks to make it easier to tune the memory density without affecting
the bandwidth (previously the only means of scaling the device count
was through the number of channels).

The patch also adds some basic sanity checks to ensure that the number
of ranks is a power of two (since we rely on bit slices in the address
decoding).
arm: Add stats to table walker

This patch adds table walker stats for:
- Walk events
- Instruction vs Data
- Page size histogram
- Wait time and service time histograms
- Pending requests histogram (per cycle) - measures dist. of L
  (p(1..) = how often busy, p(0) = how often idle)
- Squashes, before starting and after completion
mem: Add parameter to reserve MSHR entries for demand access

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.
mem: Rework the structuring of the prefetchers

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.
mem: Fix bug relating to writebacks and prefetches

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.
mem: Fix event scheduling issue for prefetches

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.
mem: Hide WriteInvalidate requests from prefetchers

Without this tweak, a prefetcher will happily prefetch data that will
promptly be invalidated and overwritten by a WriteInvalidate.
mem: Change prefetcher to use random_mt

Prefechers has used rand() to generate random numers previously.