ModelSim SE User's Manual - Electrical and Computer Engineering

UM-318 12 - Profiling performance and memory use
Introducing performance and memory profiling
A statistical sampling profiler
A memory allocation profiler
ModelSim SE User’s Manual
The profiler provides an interactive graphical representation of both memory and CPU
usage on a per instance basis. It shows you what part of your design is consuming resources
(CPU cycles or memory), allowing you to more quickly find problem areas in your code.
The profiler enables those familiar with the design and validation environment to find firstlevel
improvements in a matter of minutes. For example, the statistical sampling profiler
might show the following:
non-accelerated VITAL library cells that are impacting simulation run time
objects in the sensitivity list that are not required, resulting in a process that consumes
more simulation time than necessary
a testbench process that is active even though it is not needed
an inefficient C module
random number processes that are consuming simulation resources in a testbench running
in non-random mode
With this information, you can make changes to the VHDL or Verilog source code that will
speed up the simulation.
The memory allocation profiler provides insight into how much memory different parts of
the design are consuming. The two major areas of concern are typically: 1) memory usage
during elaboration, and 2) during simulation. If memory is exhausted during elaboration,
for example, memory profiling may provide insights into what part(s) of the design are
memory intensive. Or, if your HDL or PLI/FLI code is allocating memory and not freeing
it when appropriate, the memory profiler will indicate excessive memory use in particular
portions of the design.
The profiler’s statistical sampling profiler samples the current simulation at a userdetermined
rate (every milliseconds of real or "wall-clock" time, not simulation time)
and records what is executing at each sample point. The advantage of statistical sampling
is that an entire simulation need not be run to get good information about what parts of your
design are using the most simulation time. A few thousand samples, for example, can be
accumulated before pausing the simulation to see where simulation time is being spent.
The statistical profiler reports only on the samples that it can attribute to user code. For
example, if you use the -nodebug argument to vcom (CR-311) or vlog (CR-358), it cannot
report sample results.
The profiler’s memory allocation profiler records every memory allocation and
deallocation that takes place in the context of elaborating and simulating the design. It
makes a record of the design element that is active at the time of allocation so memory
resources can be attributed to appropriate parts of the design. This provides insights into
memory usage that can help you re-code designs to, for example, minimize memory use,
correct memory leaks, and change optimization parameters used at compile time.