ruby: dma sequencer: remove RubyPort as parent class
As of now DMASequencer inherits from the RubyPort class.  But the code in
RubyPort class is heavily tailored for the CPU Sequencer.  There are parts of
the code that are not required at all for the DMA sequencer.  Moreover, the
next patch uses the dma sequencer for carrying out memory accesses for all the
io devices.  Hence, it is better to have a leaner dma sequencer.
ruby: single physical memory in fs mode
Both ruby and the system used to maintain memory copies.  With the changes
carried for programmed io accesses, only one single memory is required for
fs simulations.  This patch sets the copy of memory that used to reside
with the system to null, so that no space is allocated, but address checks
can still be carried out.  All the memory accesses now source and sink values
to the memory maintained by ruby.
ruby: remove sparse memory.
In my opinion, it creates needless complications in rest of the code.
Also, this structure hinders the move towards common set of code for
physical memory controllers.
ruby: slicc: allow adding a bool to an int, like C++.
ruby: coherence protocols: remove data block from dirctory entry
This patch removes the data block present in the directory entry structure
of each protocol in gem5's mainline.  Firstly, this is required for moving
towards common set of memory controllers for classic and ruby memory systems.
Secondly, the data block was being misused in several places.  It was being
used for having free access to the physical memory instead of calling on the
memory controller.

From now on, the directory controller will not have a direct visibility into
the physical memory.  The Memory Vector object now resides in the
Memory Controller class.  This also means that some significant changes are
being made to the functional accesses in ruby.
ruby: remove the function functionalReadBuffers()
This function was added when I had incorrectly arrived at the conclusion
that such a function can improve the chances of a functional read succeeding.
As was later realized, this is not possible in the current setup.  While the
code using this function was dropped long back, this function was not.  Hence
the patch.
ruby: interface with classic memory controller
This patch is the final in the series.  The whole series and this patch in
particular were written with the aim of interfacing ruby's directory controller
with the memory controller in the classic memory system.  This is being done
since ruby's memory controller has not being kept up to date with the changes
going on in DRAMs.  Classic's memory controller is more up to date and
supports multiple different types of DRAM.  This also brings classic and
ruby ever more close.  The patch also changes ruby's memory controller to
expose the same interface.
ruby: provide a backing store
Ruby's functional accesses are not guaranteed to succeed as of now.  While
this is not a problem for the protocols that are currently in the mainline
repo, it seems that coherence protocols for gpus rely on a backing store to
supply the correct data.  The aim of this patch is to make this backing store
configurable i.e. it comes into play only when a particular option:
--access-backing-store is invoked.

The backing store has been there since M5 and GEMS were integrated.  The only
difference is that earlier the system used to maintain the backing store and
ruby's copy was write-only.  Sometime last year, we moved to data being
supplied supplied by ruby in SE mode simulations.  And now we have patches on
the reviewboard, which remove ruby's copy of memory altogether and rely
completely on the system's memory to supply data.  This patch adds back a
SimpleMemory member to RubySystem.  This member is used only if the option:
access-backing-store is set to true.  By default, the memory would not be
accessed.
stats: updates due to changes to ruby
cpu: Minor Draining Bug

Fixes a bug where Minor drains in the midst of committing a
conditional store.

While committing a conditional store, lastCommitWasEndOfMacroop is true
(from the previous instruction) as we still haven't finished the conditional
store. If a drain occurs before the cache response, Minor would check just
lastCommitWasEndOfMacroop, which was true, and set drainState=DrainHaltFetch,
which increases the streamSeqNum.  This caused the conditional store to be
squashed when the memory responded and it completed.  However, to the memory
the store succeeded, while to the instruction sequence it never occurred.

In the case of an LLSC, the instruction sequence will replay the squashed
STREX, which will fail as the cache is no longer in LLSC.  Then the
instruction sequence will loop back to a LDREX, which receives the updated
(incorrect) value.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>
tests: A test program for the new mwait implementation.

This is a simple test program for the new mwait implemenation. It is uses
m5threads to create to threads of execution in syscall emulation mode that
interact using the mwait instruction.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>
x86 isa: This patch attempts an implementation at mwait.

Mwait works as follows:
1. A cpu monitors an address of interest (monitor instruction)
2. A cpu calls mwait - this loads the cache line into that cpu's cache.
3. The cpu goes to sleep.
4. When another processor requests write permission for the line, it is
   evicted from the sleeping cpu's cache. This eviction is forwarded to the
   sleeping cpu, which then wakes up.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>