NOTE: These results are still very much in flux as CXXRTL is under heavy development!

Check out the "CXXRTL, A Yosys Simulation Backend" article on my blog!

Yosys CXXRTL simulation backend (Yosim?) Benchmark

This project compares the simulation speed of the following open source simulators:

• Icarus Verilog (11.0)
• Verilator (rev 4.033)
• Yosys CXXRTL (version listed with results.)

The test design is a VexRiscv CPU with some RAM and some LEDs that are toggling.

I run the simulation for 1M clock cycles, except on Icarus Verilog where I only do 100K. It's just too slow...

Prepare Verilog

(This is optional: the generated Verilog and .bin files are part of the repo.)

cd sw
make
cd ../spinal
make sim

Icarus Verilog

cd tb
make tb
time ./tb

Result (for 100K clock cycles):

...
real	0m26.389s
user	0m26.313s
sys	0m0.061s

Verilator

Verilator - No Waves
Verilator 4.033 devel rev v4.032-73-gdef40fa


real	0m0.456s
user	0m0.452s
sys	0m0.004s

real	0m0.456s
user	0m0.456s
sys	0m0.000s

real	0m0.456s
user	0m0.456s
sys	0m0.000s

Verilator - VCD
Verilator 4.033 devel rev v4.032-73-gdef40fa


real	0m9.381s
user	0m3.371s
sys	0m2.406s

real	0m7.503s
user	0m3.484s
sys	0m2.447s

real	0m7.078s
user	0m3.421s
sys	0m2.521s

CXXRTL - Max Opt

CXXRTL - Max Opt - No Waves
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m1.473s
user	0m1.472s
sys	0m0.000s

real	0m1.470s
user	0m1.469s
sys	0m0.000s

real	0m1.472s
user	0m1.467s
sys	0m0.004s

CXXRTL - Max Opt - VCD full (incl Mem)
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	1m34.634s
user	1m32.743s
sys	0m1.759s

CXXRTL - Max Opt - VCD full (no Mem)
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m9.158s
user	0m7.337s
sys	0m1.170s

CXXRTL - Max Opt - VCD regs only
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m8.517s
user	0m6.740s
sys	0m1.146s

CXXRTL - Max Debug

CXXRTL - Max Debug - No Waves
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m2.474s
user	0m2.384s
sys	0m0.008s

real	0m2.382s
user	0m2.381s
sys	0m0.000s

real	0m2.373s
user	0m2.371s
sys	0m0.000s

CXXRTL - Max Debug - VCD full (incl Mem)
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	2m3.533s
user	1m58.238s
sys	0m4.685s

CXXRTL - Max Debug - VCD full (no Mem)
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m39.661s
user	0m33.152s
sys	0m5.129s

CXXRTL - Max Debug - VCD regs only
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m10.470s
user	0m7.970s
sys	0m1.659s

CXXRTL - Compiler Versions

CXXRTL - Max Opt - clang9
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m1.488s
user	0m1.474s
sys	0m0.012s

real	0m1.473s
user	0m1.472s
sys	0m0.000s

real	0m1.461s
user	0m1.457s
sys	0m0.004s

CXXRTL - Max Opt - clang6
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m1.455s
user	0m1.444s
sys	0m0.004s

real	0m1.450s
user	0m1.445s
sys	0m0.004s

real	0m1.447s
user	0m1.446s
sys	0m0.000s

CXXRTL - Max Opt - gcc10.1
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m1.736s
user	0m1.729s
sys	0m0.000s

real	0m1.726s
user	0m1.717s
sys	0m0.008s

real	0m1.727s
user	0m1.726s
sys	0m0.000s

CXXRTL - Max Opt - gcc7.5
Yosys 0.9+2406 (git sha1 334ec5fa, clang 6.0.0-1ubuntu2 -fPIC -Os)


real	0m1.688s
user	0m1.678s
sys	0m0.004s

real	0m1.678s
user	0m1.677s
sys	0m0.000s

real	0m1.674s
user	0m1.673s
sys	0m0.000s

CXXRTL Recipe

At the time of writing this, the cxxrtl optimization recipe was as follows:

read_verilog ../spinal/ExampleTop.sim.v
hierarchy -check -top ExampleTop
write_ilang ExampleTop.sim.ilang
write_cxxrtl ExampleTop.sim.cpp

Verilator Compile Time

real	0m3.671s
user	0m3.221s
sys	0m0.138s

CXXRTL Compile Time

clang9 not only gives the best simulation results, but it also compiles must faster than anything else.

Compile time example_default_clang9

real	0m7.321s
user	0m6.976s
sys	0m0.183s


Compile time example_Og_clang9

real	0m9.195s
user	0m9.020s
sys	0m0.142s


Compile time example_default_clang6

real	0m17.038s
user	0m16.562s
sys	0m0.181s


Compile time example_default_gcc10

real	0m32.420s
user	0m31.701s
sys	0m0.497s


Compile time example_default_gcc7

real	0m19.918s
user	0m19.277s
sys	0m0.425s