This patch adds the following two methods to the Drainable base class:
memWriteback() - Write back all dirty cache lines to memory using
functional accesses.
memInvalidate() - Invalidate memory system buffers. Dirty data
won't be written back.
Specifying calling memWriteback() after draining will allow us to
checkpoint systems with caches. memInvalidate() can be used to drop
memory system buffers in preparation for switching to an accelerated
CPU model that bypasses the gem5 memory system (e.g., hardware
virtualized CPUs).
Note: This patch only adds the methods to Drainable, the code for
flushing the TLB and the cache is committed separately.
This patch moves the draining interface from SimObject to a separate
class that can be used by any object needing draining. However,
objects not visible to the Python code (i.e., objects not deriving
from SimObject) still depend on their parents informing them when to
drain. This patch also gets rid of the CountedDrainEvent (which isn't
really an event) and replaces it with a DrainManager.
