sim: Add a mechanism to exit the simulation loop immediately.

There are some cases, specifically when running systemc, that it's
necessary to exit the simulation loop immediately rather than finishing
running events scheduled for the current Tick. When running under
sc_main, sc_stop and sc_pause return control to sc_main which can
happen immediately. When running without sc_main, control needs to
return to the python config script which needs to happen through a
global exit event.

Since sc_pause and sc_stop are supposed to stop simulation without
necessarily letting all the events at the current time run, we need
a way to schedule an exit event with a very high priority (rather than
a very low priority).

This change adds a new exitSimLoopNow function which does that, and
adds a new constructor to the GlobalSimLoopExitEvent which uses that
priority.

Also, a couple of cruft functions from the sim events are removed.

Change-Id: Icfbec17fb10f98084a75740acd839dbf4096fbb3
Reviewed-on: https://gem5-review.googlesource.com/c/16444
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

style: [patch 3/22] reduce include dependencies in some headers

Used cppclean to help identify useless includes and removed them. This
involved erroneously included headers, but also cases where forward
declarations could have been used rather than a full include.

sim: simulate with multiple threads and event queues
This patch adds support for simulating with multiple threads, each of
which operates on an event queue. Each sim object specifies which eventq
is would like to be on. A custom barrier implementation is being added
using which eventqs synchronize.

The patch was tested in two different configurations:
1. ruby_network_test.py: in this simulation L1 cache controllers receive
requests from the cpu. The requests are replied to immediately without
any communication taking place with any other level.
2. twosys-tsunami-simple-atomic: this configuration simulates a client-server
system which are connected by an ethernet link.

We still lack the ability to communicate using message buffers or ports. But
other things like simulation start and end, synchronizing after every quantum
are working.

Committed by: Nilay Vaish

sim: added option to serialize SimLoopExitEvent

SimLoopExitEvents weren't serialized by default. Some benchmarks
utilize a delayed m5 exit pseudo op call to terminate the simulation
and this event was lost when resuming from a checkpoint generated
after the pseudo op call. This patch adds the capability to serialize
the SimLoopExitEvents and enable serialization for m5_exit and m5_fail
pseudo ops by default. Does not affect other generic
SimLoopExitEvents.

Replace curTick global variable with accessor functions.
This step makes it easy to replace the accessor functions
(which still access a global variable) with ones that access
per-thread curTick values.

pseudoinst: get rid of mainEventQueue references.
Avoid direct references to mainEventQueue in pseudo-insts
by indirecting through associated CPU object.
Made exitSimLoop() more flexible to enable some of these.

types: Move stuff for global types into src/base/types.hh

eventq: convert all usage of events to use the new API.
For now, there is still a single global event queue, but this is
necessary for making the steps towards a parallelized m5.

there are two main thrusts of this changeset.

1) return the periodicity of checkpoints back into the code (i.e. make m5 checkpoint n m meaningful again).
2) to do this, i had to much around with being able to repeatedly schedule and SimLoopExitEvent, which led to changes in how exit simloop events are handled to make this easier.

src/arch/alpha/isa/decoder.isa:
src/mem/cache/cache_impl.hh:
modify arg. order for new calling convention of exitSimLoop.
src/cpu/base.cc:
src/sim/main.cc:
src/sim/pseudo_inst.cc:
src/sim/root.cc:
now, instead of creating a new SimLoopExitEvent, call a wrapper schedExitSimLoop which handles all the default args.
src/sim/sim_events.cc:
src/sim/sim_events.hh:
src/sim/sim_exit.hh:
add the periodicity of checkpointing back into the code.

to facilitate this, there are now two wrappers (instead of just overloading exitSimLoop). exitSimLoop is only for exiting NOW (i.e. at curTick), while schedExitSimLoop schedules and exit event for the future.

Move main control from C++ into Python.
User script now invokes initialization and
simulation loop after building configuration.
These functions are exported from C++ to Python
using SWIG.

SConstruct:
Set up SWIG builder & scanner.
Set up symlinking of source files into build directory
(by not disabling the default behavior).
configs/test/test.py:
Rewrite to use new script-driven interface.
Include a sample option.
src/SConscript:
Set up symlinking of source files into build directory
(by not disabling the default behavior).
Add SWIG-generated main_wrap.cc to source list.
src/arch/SConscript:
Set up symlinking of source files into build directory
(by not disabling the default behavior).
src/arch/alpha/ev5.cc:
src/arch/alpha/isa/decoder.isa:
src/cpu/o3/alpha_cpu_impl.hh:
src/cpu/trace/opt_cpu.cc:
src/cpu/trace/trace_cpu.cc:
src/sim/pseudo_inst.cc:
src/sim/root.cc:
src/sim/serialize.cc:
src/sim/syscall_emul.cc:
SimExit() is now exitSimLoop().
src/cpu/base.cc:
SimExitEvent is now SimLoopExitEvent
src/python/SConscript:
Add SWIG build command for main.i.
Use python/m5 in build dir as source for zip archive...
easy now with file duplication enabled.
src/python/m5/__init__.py:
- Move copyright notice back to C++ so we can print
it right away, even for interactive sessions.
- Get rid of argument parsing code; just provide default
option descriptors for user script to call optparse with.
- Don't clutter m5 namespace by sucking in all of m5.config
and m5.objects.
- Move instantiate() function here from config.py.
src/python/m5/config.py:
- Move instantiate() function to __init__.py.
- Param.Foo deferred type lookups must use m5.objects
namespace now (not m5).
src/python/m5/objects/AlphaConsole.py:
src/python/m5/objects/AlphaFullCPU.py:
src/python/m5/objects/AlphaTLB.py:
src/python/m5/objects/BadDevice.py:
src/python/m5/objects/BaseCPU.py:
src/python/m5/objects/BaseCache.py:
src/python/m5/objects/Bridge.py:
src/python/m5/objects/Bus.py:
src/python/m5/objects/CoherenceProtocol.py:
src/python/m5/objects/Device.py:
src/python/m5/objects/DiskImage.py:
src/python/m5/objects/Ethernet.py:
src/python/m5/objects/Ide.py:
src/python/m5/objects/IntrControl.py:
src/python/m5/objects/MemObject.py:
src/python/m5/objects/MemTest.py:
src/python/m5/objects/Pci.py:
src/python/m5/objects/PhysicalMemory.py:
src/python/m5/objects/Platform.py:
src/python/m5/objects/Process.py:
src/python/m5/objects/Repl.py:
src/python/m5/objects/Root.py:
src/python/m5/objects/SimConsole.py:
src/python/m5/objects/SimpleDisk.py:
src/python/m5/objects/System.py:
src/python/m5/objects/Tsunami.py:
src/python/m5/objects/Uart.py:
Fix up imports (m5 namespace no longer includes m5.config).
src/sim/eventq.cc:
src/sim/eventq.hh:
Support for Python-called simulate() function:
- Use IsExitEvent flag to signal events that want
to exit the simulation loop gracefully (instead of
calling exit() to terminate the process).
- Modify interface to hand exit event object back to
caller so it can be inspected for cause.
src/sim/host.hh:
Add MaxTick constant.
src/sim/main.cc:
Move copyright notice back to C++ so we can print
it right away, even for interactive sessions.
Use PYTHONPATH environment var to set module path
(instead of clunky code injection method).
Move main control from here into Python:
- Separate initialization code and simulation loop
into separate functions callable from Python.
- Make Python interpreter invocation more pure (more
like directly invoking interpreter).
Add -i and -p flags (only options on binary itself;
other options processed by Python).
Import readline package when using interactive mode.
src/sim/sim_events.cc:
SimExitEvent is now SimLoopExitEvent, and uses
IsSimExit flag to terminate loop (instead of
exiting simulator process).
src/sim/sim_events.hh:
SimExitEvent is now SimLoopExitEvent, and uses
IsSimExit flag to terminate loop (instead of
exiting simulator process).
Get rid of a few unused constructors.
src/sim/sim_exit.hh:
SimExit() is now exitSimLoop().
Get rid of unused functions.
Add comments.

Updated Authors from bk prs info

New directory structure:
- simulator source now in 'src' subdirectory
- imported files from 'ext' repository
- support building in arbitrary places, including
outside of the source tree. See comment at top
of SConstruct file for more details.
Regression tests are temporarily disabled; that
syetem needs more extensive revisions.

SConstruct:
Update for new directory structure.
Modify to support build trees that are not subdirectories
of the source tree. See comment at top of file for
more details.
Regression tests are temporarily disabled.
src/arch/SConscript:
src/arch/isa_parser.py:
src/python/SConscript:
Update for new directory structure.