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Andreas Hansson ea5ccc7041 mem: Clean up packet data allocation 
This patch attempts to make the rules for data allocation in the
packet explicit, understandable, and easy to verify. The constructor
that copies a packet is extended with an additional flag "alloc_data"
to enable the call site to explicitly say whether the newly created
packet is short-lived (a zero-time snoop), or has an unknown life-time
and therefore should allocate its own data (or copy a static pointer
in the case of static data).

The tricky case is the static data. In essence this is a
copy-avoidance scheme where the original source of the request (DMA,
CPU etc) does not ask the memory system to return data as part of the
packet, but instead provides a pointer, and then the memory system
carries this pointer around, and copies the appropriate data to the
location itself. Thus any derived packet actually never copies any
data. As the original source does not copy any data from the response
packet when arriving back at the source, we must maintain the copy of
the original pointer to not break the system. We might want to revisit
this one day and pay the price for a few extra memcpy invocations.

All in all this patch should make it easier to grok what is going on
in the memory system and how data is actually copied (or not).
2014-12-02 06:07:54 -05:00
build_opts alpha: Stop using 'inorder' and rely entirely on 'minor' 2014-09-03 07:42:56 -04:00
configs config, kvm: Enabling KvmCPU in SE mode 2014-11-23 18:01:08 -08:00
ext ext: Bump DRAMPower to avoid compilation issues 2014-10-20 18:03:53 -04:00
src mem: Clean up packet data allocation 2014-12-02 06:07:54 -05:00
system arm: Add support for ARMv8 (AArch64 & AArch32) 2014-01-24 15:29:34 -06:00
tests stats: Bump stats after static analysis fixes 2014-11-24 09:03:39 -05:00
util kvm, x86: Adding support for SE mode execution 2014-11-23 18:01:08 -08:00
.hgignore ext: Add a McPAT regression tester 2014-06-04 07:48:20 -07:00
.hgtags Added tag stable_2014_08_26 for changeset cb2e6950956d 2014-08-26 14:41:23 -05:00
COPYING copyright: Add code for finding all copyright blocks and create a COPYING file 2011-06-02 17:36:07 -07:00
LICENSE copyright: Add code for finding all copyright blocks and create a COPYING file 2011-06-02 17:36:07 -07:00
README misc: README direct to website for dependencies 2014-08-26 10:12:04 -04:00
SConstruct config: Add the ability to read a config file using C++ and Python 2014-10-16 05:49:37 -04:00

README 

This is the gem5 simulator.

The main website can be found at http://www.gem5.org

A good starting point is http://www.gem5.org/Introduction, and for
more information about building the simulator and getting started
please see http://www.gem5.org/Documentation and
http://www.gem5.org/Tutorials.

To build gem5, you will need the following software: g++ or clang,
Python (gem5 links in the Python interpreter), SCons, SWIG, zlib, m4,
and lastly protobuf if you want trace capture and playback
support. Please see http://www.gem5.org/Dependencies for more details
concerning the minimum versions of the aforementioned tools.

Once you have all dependencies resolved, type 'scons
build/<ARCH>/gem5.opt' where ARCH is one of ALPHA, ARM, NULL, MIPS,
POWER, SPARC, or X86. This will build an optimized version of the gem5
binary (gem5.opt) for the the specified architecture. See
http://www.gem5.org/Build_System for more details and options.

With the simulator built, have a look at
http://www.gem5.org/Running_gem5 for more information on how to use
gem5.

The basic source release includes these subdirectories:
   - configs: example simulation configuration scripts
   - ext: less-common external packages needed to build gem5
   - src: source code of the gem5 simulator
   - system: source for some optional system software for simulated systems
   - tests: regression tests
   - util: useful utility programs and files

To run full-system simulations, you will need compiled system firmware
(console and PALcode for Alpha), kernel binaries and one or more disk
images. Please see the gem5 download page for these items at
http://www.gem5.org/Download

If you have questions, please send mail to gem5-users@gem5.org

Enjoy using gem5 and please share your modifications and extensions.