Still some remains of the --threads 0 mode. Remove unnecessary complexity
from V3EmitCModel. (Also don't pretend there is an MTask in single
threaded mode, when there really isn't.)
It's unlikely one value fits all use case, so making VL_LOCK_SPINS
configurable at model build time.
For testing, we reduce the value as we expect high contention.
This API is used if the user copies the process using `fork`
and similar OS-level mechanisms. The `at_clone` member function
ensures that all model-allocated resources are re-allocated, such
that the copied child process/model can simulate correctly.
A typical allocated resource is the thread pool, which every model
has its own pool.
Pack the elements of VlTriggerVec as dense bits (instead of a 1 byte
bool per bit), and check whether they are set on a word granularity.
This effectively transforms conditions of the form `if (trig.at(0) |
trig.at(2) | trig.at(64))` into `if (trig.word(0) & 0x5 | trig.word(1) &
0x1)`. This improves OpenTitan ST by about 1%, worth more on some other
designs.
All remaining use of conditional compilation in the tracing
implementation of the run-time library are replaced with the use of
VerilatedModel::traceConfig, and is now done at run-time.
VCD tracing is now parallelized using the same thread pool as the model.
We achieve this by breaking the top level trace functions into multiple
top level functions (as many as --threads), and after emitting the time
stamp to the VCD file on the main thread, we execute the tracing
functions in parallel on the same thread pool as the model (which we
pass to the trace file during registration), tracing into a secondary
per thread buffer. The main thread will then stitch (memcpy) the buffers
together into the output file.
This makes the `--trace-threads` option redundant with `--trace`, which
now only affects `--trace-fst`. FST tracing uses the previous offloading
scheme.
This obviously helps a lot in VCD tracing performance, and I have seen
better than Amdahl speedup, namely I get 3.9x on XiangShan 4T (2.7x on
OpenTitan 4T).
Wilson Snyder
Todd Strader
Marlon James
Geza Lore
Yinan Xu
Mariusz Glebocki
Eyck Jentzsch
Kamil Rakoczy
Andrew Nolte
Larry Doolittle