CEA-LIST / csram-qemu-plugin

QEMU plugin for C-SRAM functionnal emulation

CSRAM qemu plugin

This is a QEMU plugin which emulates the Computational SRAM (C-SRAM).

C-SRAM is a domain-specific near-memory computing architecture grouping a subset of energy-optimized operations. This near-memory computing architecture allows an optimized coupling between SRAM and vector-ALU based on a custom ISA requiring a specific programming. Thus, the C-SRAM could be used as a programmable vector processing unit driven by the host scalar processor and as a low-latency SRAM (e.g. TCM or scratchpad) the rest of the time. This privileged mode of use drastically reduces energy consumption by minimizing the data movement (limited number of Load/Store) as well as the code size.

It emulates the functional behavior of the C-SRAM and allows to evaluate full application performance.

It contains instructions count per categories (memory access instructions, scalar instructions, vector instructions) for RISCV-based system and a system with a C-SRAM and RISCV processor

How to build and install

• make getQemuSrc all
• make demo
• make install (adapt the INSTALLDIR in the makefile)

The demo target should show the result for an addition of two vectors:

make demo
riscv32-unknown-linux-gcc -o CxRAM-SimpleAdd CxRAM-SimpleAdd.c
qemu-riscv32 -plugin ./libCxRAM-qemu-plugin.so CxRAM-SimpleAdd 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
   001  002  003  004  005  006  007  008  009  010  011  012  013  014  015  016
-  042  042  042  042  042  042  042  042  042  042  042  042  042  042  042  042
=  043  044  045  046  047  048  049  050  051  052  053  054  055  056  057  058

How to use

QEMU can use a plugin with two flavors :

• With a -plugin ./libCxRAM-qemu-plugin.so flag
• With the QEMU_PLUGIN shell environment variable containing the full file name of the plugin. The later is used in the HybroGen environment available here: https://github.com/CEA-LIST/HybroGen.

Get Report, Trace and Verbose

Report

Using the environment variable QEMU_CXRAM_REPORT, it will generate a performance report perf_report.csv with nb ops, latancy and energy used by the system.

Activate this functionality with export QEMU_CXRAM_REPORT="yes" and desactivate it with unset QEMU_CXRAM_REPORT

/!\ The performance and energy model available online is completely artificial and does not reflect the performance of any C-SRAM circuit

Trace

Using the environment variable QEMU_CXRAM_TRACE, it will show all executed C-SRAM instructions and the data in memory before and after the execution of instructions:

in1:  1   1   1   1   1   1   1   1   1   1   1   1   1   1   1   1 
in2: 42  42  42  42  42  42  42  42  42  42  42  42  42  42  42  42 
res:  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0 
Decode CxRAM operation _cm_add8_mmm
res: 43  43  43  43  43  43  43  43  43  43  43  43  43  43  43  43 

Activate this functionality with export QEMU_CXRAM_TRACE="yes" and desactivate it with unset QEMU_CXRAM_TRACE

Verbose

Using the environment variable QEMU_CXRAM_VERBOSE, it will show all plugin function call.

Activate this functionality with export QEMU_CXRAM_TRACE="yes" and desactivate with unset QEMU_CXRAM_TRACE

Authors

• Thaddée BRICOUT
• Kevin MAMBU
• Henri-Pierre CHARLES