cpu: Replace the fastmem with a new CPU model

The AtomicSimpleCPU used to be able to access memory directly to speed
up simulation if no caches are used. This is fine as long as no
switching between CPU models is required. In order to switch to a new
CPU model that requires caches, we currently need to checkpoint the
system and restore it into a new configuration. The new
'atomic_noncaching' memory mode provides a solution that avoids this
issue since caches are bypassed in this mode. This changeset removes
the old fastmem option from the AtomicSimpleCPU and introduces a new
CPU, NonCachingSimpleCPU, which derives from the AtomicSimpleCPU.

The NonCachingSimpleCPU uses the same mechanism as the AtomicSimpleCPU
used to use when accessing memory in when fastmem was enabled.

This changeset also introduces a new switcheroo test that tests
switching between a NonCachingSimpleCPU and a TimingSimpleCPU with
caches.

Change-Id: If01893f9b37528b14f530c11ce6f53c097582c21
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/12419
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

4 files changed, 5 insertions, 27 deletions

diff --git a/configs/common/CpuConfig.py b/configs/common/CpuConfig.py
index d70e6cfa7..f0d009e95 100644
--- a/configs/common/CpuConfig.py
+++ b/configs/common/CpuConfig.py
@@ -69,6 +69,7 @@ def _cpu_subclass_tester(name):
     return tester
 
 is_kvm_cpu = _cpu_subclass_tester("BaseKvmCPU")
+is_atomic_cpu = _cpu_subclass_tester("AtomicSimpleCPU")
 
 def get(name):
     """Get a CPU class from a user provided class name or alias."""
diff --git a/configs/common/Options.py b/configs/common/Options.py
index 29ef74c9a..aed888191 100644
--- a/configs/common/Options.py
+++ b/configs/common/Options.py
@@ -164,8 +164,6 @@ def addCommonOptions(parser):
     parser.add_option("-l", "--lpae", action="store_true")
     parser.add_option("-V", "--virtualisation", action="store_true")
 
-    parser.add_option("--fastmem", action="store_true")
-
     # dist-gem5 options
     parser.add_option("--dist", action="store_true",
                       help="Parallel distributed gem5 simulation.")
diff --git a/configs/example/fs.py b/configs/example/fs.py
index f299d761c..3997ed76c 100644
--- a/configs/example/fs.py
+++ b/configs/example/fs.py
@@ -188,22 +188,13 @@ def build_test_system(np):
             test_sys.iobridge.master = test_sys.membus.slave
 
         # Sanity check
-        if options.fastmem:
-            if TestCPUClass != AtomicSimpleCPU:
-                fatal("Fastmem can only be used with atomic CPU!")
-            if (options.caches or options.l2cache):
-                fatal("You cannot use fastmem in combination with caches!")
-
         if options.simpoint_profile:
-            if not options.fastmem:
-                # Atomic CPU checked with fastmem option already
-                fatal("SimPoint generation should be done with atomic cpu and fastmem")
+            if not CpuConfig.is_atomic_cpu(TestCPUClass):
+                fatal("SimPoint generation should be done with atomic cpu")
             if np > 1:
                 fatal("SimPoint generation not supported with more than one CPUs")
 
         for i in xrange(np):
-            if options.fastmem:
-                test_sys.cpu[i].fastmem = True
             if options.simpoint_profile:
                 test_sys.cpu[i].addSimPointProbe(options.simpoint_interval)
             if options.checker:
@@ -269,8 +260,6 @@ def build_drive_system(np):
     drive_sys.cpu.createThreads()
     drive_sys.cpu.createInterruptController()
     drive_sys.cpu.connectAllPorts(drive_sys.membus)
-    if options.fastmem:
-        drive_sys.cpu.fastmem = True
     if options.kernel is not None:
         drive_sys.kernel = binary(options.kernel)
 
diff --git a/configs/example/se.py b/configs/example/se.py
index 015a953da..804ef02c5 100644
--- a/configs/example/se.py
+++ b/configs/example/se.py
@@ -213,16 +213,9 @@ if CpuConfig.is_kvm_cpu(CPUClass) or CpuConfig.is_kvm_cpu(FutureClass):
         fatal("KvmCPU can only be used in SE mode with x86")
 
 # Sanity check
-if options.fastmem:
-    if CPUClass != AtomicSimpleCPU:
-        fatal("Fastmem can only be used with atomic CPU!")
-    if (options.caches or options.l2cache):
-        fatal("You cannot use fastmem in combination with caches!")
-
 if options.simpoint_profile:
-    if not options.fastmem:
-        # Atomic CPU checked with fastmem option already
-        fatal("SimPoint generation should be done with atomic cpu and fastmem")
+    if not CpuConfig.is_atomic_cpu(TestCPUClass):
+        fatal("SimPoint/BPProbe should be done with an atomic cpu")
     if np > 1:
         fatal("SimPoint generation not supported with more than one CPUs")
 
@@ -234,9 +227,6 @@ for i in xrange(np):
     else:
         system.cpu[i].workload = multiprocesses[i]
 
-    if options.fastmem:
-        system.cpu[i].fastmem = True
-
     if options.simpoint_profile:
         system.cpu[i].addSimPointProbe(options.simpoint_interval)