HybridSim

University of Maryland, College Park
Memory Systems Research Lab
Lead Developer: Jim Stevens

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Description:

HybridSim is a timing simulation for a memory system design that
utilizes a DRAM memory subsystem to cache a non-volatile memory. The DRAM
subsystem is simulated by DRAMSim2 and the NVRAM subsystem is simulated
by NVDIMMSim. HybridSim can run as a standalone trace-based simulator or
as part of a full system simulator.

HybridSim assumes the cache controller exists on the CPU and can be
accessed with no overhead. The cache tag lookup delay in HybridSim is
configurable.  HybridSim simulates accesses at a granularity of 64 bytes
(the last level cache line size that is typically used as the memory
system access granularity). Each of these lines is then part of a larger
NVDIMM page (typically 4K, but configurable).  When a page is mapped
into the DRAM, HybridSim simply passes accesses along to DRAMSim2 to
simulate the timing. When a page is not mapped into the DRAM, HybridSim
evicts a page from the cache set and then requests the missed page from
the NVDIMM. HybridSim is lockup free, so while one DRAM cache miss is
being serviced, other accessed can continue without delay.

HybridSim also has support for sequential prefetching and perfect
prefetching (prefetching based on a prefetch script computed ahead
of time).

It is important to note that this is an experimental research codebase.
This is not guaranteed to run on any platform outside of our development
and experiment machines (we run Ubuntu 10.04 and 12.04). If you want to
support another platform, feel free to make whatever changes are necessary
and generate a patch. As long as it doesn't break things in our setup,
then we will gladly merge it. Additionally, all of our memory simulators
contain many experimental features that are not guaranteed to work
well in all situations. Please contact the development team if you have
questions about how certain features work or how to make the simulators
work well for your goals. 

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Build instructions:

To build HybridSim, the external headers and .so files for DRAMSim and
NVDIMMSim must be available. NVDIMMSim must be placed in the ../NVDIMMSim
directory and DRAMSim2 must be placed in the ../DRAMSim2 directory
relative to this directory. Follow the instructions for those systems to
build the .so files. Then, to build the standalone trace-based simulator,
simply type "make".

To build HybridSim as a shared library, type "make lib". The marss.hybridsim repo
can then be built with libhybridsim.so.

All code mentioned above can be found at:
https://github.com/jimstevens2001


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Trace-Based Simulator Usage:

./HybridSim <trace-file>

The trace file format is an ASCII file with each access in the trace as a separate
line. Each access consists of a cycle number, an operation type (0 for read, 1 for write),
and an byte address for the memory access (addresses should be aligned to 64 bytes).

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Repository Management:

This repo follows a standard git branching scheme.

* master - stable branch
* dev - unstable development branch

All other branches are feature branches. Some may be orphans and some
may eventually be merged into dev. The master branch will only merge
changes from dev after we are satisfied they are stable.

Tags with format vX.Y.Z are considered releases of stable versions.
All other tags are considered experimental.

The following versions of NVDIMMSim and DRAMSim2 will be kept compatible with
the master branch of HybridSim...

https://github.com/jimstevens2001/NVDIMMSim/tree/stable
https://github.com/jimstevens2001/DRAMSim2

Note that the HybridSim-compatible version of DRAMSim2 is not necsesarily
the same as the mainline version of DRAMSim2 maintained here:
https://github.com/dramninjasUMD/DRAMSim2

Additionally, tagged releases across the three will be kept consistent in terms
of version numbers.

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Software License:
This software is open-source and is released under the BSD license. Please
see the file LICENSE for a copy of the license.