Document 242681
Why Use Simulation?
Simics & dark2 Assignment 1
Understanding real systems
More inspectable
Less dangerous
Fault injection
Debugging
Prototype HW before expensive
implementations
Håkan Zeffer
Uppsala University, Sweden
zeffer@it.uu.se
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What is a Simulator?
Full-System Simulation
What to simulate? Instructions,
memory etc.
What happens when an operating
system boots, traps, disk accesses etc.
Simulation vs. Emulation
User program
Libraries
Database
IDE
ISA
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Real OS &
Software
Network
PCI
RAM
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Middleware
Operating system
CPU
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ROM
(Flash)
Disk
Simulated
hardware
LCD
Devices
Hardware
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Advantages with Full
System Simulation
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OS debugging (such as, single stepping
during boot, break on traps etc.).
Performance tuning of applications and
operating systems
Fault injection
Teaching and research
Checkpointing
Determinism
Non intrusive – inspect without effecting
state
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Possible Problems
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Wisconsin Experiments
Can I trust the results that my
simulator have produced?
How do I verify my results?
Wisconsin experiments
Cycles Per Trans. (millions)
4.0
max
avg
min
3.5
3.0
2.5
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ROB Size
64
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Speed vs. Accuracy
Virtutech AB - Simics
Spice, etc
Virtutech is a small Swedish company.
25-30 persons. Office in Stockholm,
Uppsala and U.S.
Simics is the only full system simulator
that supports multiple targets and is
capable of booting unmodified
operating systems.
gate/RTL model
(>1,000,000x)
accuracy
“cycle-accurate”
architecture simulator
(>10,000x)
emulator
(~5x)
Simics™
Virtual PC, VMWare,
Crusoe, etc.
1 KIPS
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100 MIPS
speed
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Simics’s Three Modes
Fast mode: No cache simulation. Just
in time compilation (code name turbo).
Normal mode: Simple cache
simulation.
Out-of-order mode: MAI (Micro
Architecture Interface). Supports
speculative execution, such as, branch
and value prediction. Cache simulation
etc.
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Supported architectures
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X86 (from 486 to Pentium4)
AMD-64 (Hammer/Opteron)
Itanium
SUN SunFire & Serengeti (USII & USIII)
PowerPC
Alpha
ARM, MIPS + lots of devices
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Unmodified OSs
tested/supported
Windows (XP, NT, 98, 95 and more)
Solaris 9 (and more)
Linux
Tru64
VxWorks
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Linux on
Itanium
Solaris on Sun
SunFire
Windows XP/64 on
AMD Hammer
Linux
on x86
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CPU
CPU
CPU
$$$
$$$
$$$
$$$
SCSI
RAM
Arbitrary
configurations
Multiple processors
Multiple nodes
Multiple address
spaces
Arbitrary device
configurations
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© Håkan Zeffer | zeffer@it.uu.se
Applications
Operating
System
Firmware
Simics
configuration
event handling
memory
VHDL
simulator
memory bus
target machine
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Simics Architecture
Programming Interface (Simics API)
CPU
All running on a
Linux host
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Simulating Multiprocessors
Windows NT
on x86
VxWorks on
PowerPC
interpreter
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graphics
devices
Ethernet
SCSI
disks
MMU
other
Simics
process
CLI
Simics
Central
scripting
tracing
debugger
cache models
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local
disk
real
network
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Simics Dir Structure
Target vs. Host
Most of the files in the user dir install dir are soft links:
LICENSE
Makefile.in
README
README.SOURCE
README.previous
README.proxy
README_1.8
Version
configure
doc
licenses
master-install
The target is the simulated system
The host is the computer that runs
Simics
The different prompts:
- the targets prompt: root on the
target system
host$ - the host prompt: user on the host
system (xterm etc.).
simics> - the Simics prompt
Real but for this course uninteresting files:
import
scripts
config
target#
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Interesting dirs:
home
- home for different configurations. We will use the
sarek configuration
src
- simics module source code
v9-sol8-64
- binaries and build place
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simics> c
Causes Simics to run another 1000 machine
instructions and then stop.
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Simics.
simics> load-module
Load
Gives help on selected topics. Try it out!
This help command will list all commands created
for this assignment.
simics> q
Quit
a module into Simics.
simics> list-modules
Prints
a list of available modules and their
current status, loaded or not.
simics> help dark2-cache
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simics> help
Causes Simics to continue its simulation.
Pressing Ctrl-c when Simics is running causes it to
stop.
simics> c 1000
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Simics Commands (cont)
Simics Commands
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hostfs
hostfs is a virtutech module that makes it
possible to mount the host’s file system in the
simulated target’s operating system.
A module can register multiple classes
A class can register multiple attributes
The configuration system uses classes
and attributes for:
target# mount /host
Simics API
hostfs – accessing host files
This will mount the host’s file system under /host
on the target. The hostfs module has to be
loaded (module-load hostfs).
Checkpointing
target# ls /host/it/kurs/dark2
Python
command wrapping
And more...
This will list the contents on the host machine’s
file system at /stud/it/dark2
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Register a class
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Register an attribute
conf_class_t *
int
SIM_register_class(const char
*name,
class_data_t
SIM_register_attribute(conf_class_t
*class_data);
const char
get_attr_t
lang_void
Example:
static conf_class_t
static class_data_t
set_attr_t
*my_class;
lang_void
my_class_data;
my_class = SIM_register_class(”my-class-name”,
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*class_struct,
*attr_name,
get_attr,
*get_attr_data,
set_attr,
*set_attr_data,
attr_attr_t
attr,
const char
*doc);
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&my_class_data);
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© Håkan Zeffer | zeffer@it.uu.se
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Simics Command Files
Adding New Commands
The file dark2-cache.simics contains the following:
Edit the commands.py file in the dark2-cache dir
read-configuration /it/kurs/dark2/simics-checkpoints/booted-sarek-1p
def dc_resize_cmd(dc, size, block_size):
dc.size = size;
dc.block_size = block_size;
@SIM_new_object("dark2-cache", "dc0")
@conf.dc0.size = 512
@conf.dc0.block_size = 64
@conf.phys_mem0.timing_model = conf.dc0
new_command("resize", dc_resize_cmd,
[arg(integer_t, "size"), arg(integer_t, ”block-size")],
namespace = "dark2-cache",
type ="dark2-cache commands",
short="resize the cache",
doc = """
Resize the cache. The long version
""");
Command files can contain any Simics commands
Lines that starts with @ are interpreted by the Simics Python
virtual machine.
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”@conf.dc0.size = 512” calles the set-attribute function
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STC
Simics uses a fast address cache called
ISTC and DSTC for instructions resp.
data accesses.
Direct mapped SW cache containing
”safe” address translations
No
traps are possible, that is, TLB and
cache hit is guaranteed.
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This caching have to be disabled when
cache simulations are performed.
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HAP (happening)
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There are multiple haps that a user can
register callbacks for.
Initial-configuration – makes it possible to
get a callback when the configuration phase
is over.
Magic-instruction – makes it possible to get a
callback when such an instruction is
executed. This is for example done in the
magic-break-enable and magic-breakdisable commands.
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The Step- and Time-Queue
Simics uses two queues that events can
be posted on.
The STEP QUEUE: incremented on
instruction completions and interrupt
events
The TIME QUEUE: incremented each
cycle
The time queue is used when the outof-order mode are used.
The Assignment
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Questions?
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