[Iverilog-devel] Running ivtest on multiple cores

[Maciej S. <mac...@ce...>]

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Hi,

I would like to ask for your opinion about executing the ivtest suite
on parallel cores. I have modified the vvp_reg.pl script [1], so it
can use multiple instances of vvp at the same time.

The script uses Parallel::ForkManager (available in CPAN) to run
iverilog & vvp instances in separate processes to decrease the time
required to perform tests on modern CPUs.
I have managed to go down from ~1 minute to ~15 seconds on 8-core i7
with SSD. The approximate performance boost increases linearly up to 4
cores, then the difference becomes insignificant.
You may specify the number of used processes by modifying the CPUS
environmental variable, e.g. "CPUS=8 ./par_vvp_reg.pl" runs with 8
processes. Otherwise the number of available cores is autodetected
(works only in Linux, relies on /proc/cpuinfo).

Unfortunately, there are drawbacks too:
* I modified fscanf* tests, because they were using the same file and
therefore stayed in conflict. It does not change results for the
default vvp_reg.pl script. It is an example of restrictions that test
writers would have to obey.
* The output is not fully compatible with the default output stored in
the repository. I decided to sort the test results in lexical order,
otherwise the order would be random each run (depends on the time when
a test ends).
* There are two tests (pr2509349a & sys_func_task_error) that I could
not fix. I guess this might be a result of changing the iverilog
output file name from vsim to $tname.vsim (to avoid conflicts). I did
not modified them, because I do not want to break the default test
scripts.
* Output files are saved in the main directory, they are removed at
the end of the script. I do not remove ivl_vhdl_work directory between
tests, because it could be used in another process. More elegant
solution would be to use separate directories. If you think this is
completely wrong - please let me know.
* This is the first time I write code in Perl, therefore I am not sure
if everything is done in accordance with the art.

With all the mentioned shortcomings, I think that it might be a good
tool for quick, preliminary checks that could save developer's time.
What do you think?

Regards,
Orson

[1] https://github.com/orsonmmz/ivtest/tree/parallel_test
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