TotalView Users Guide - CI Wiki

Defining Eval Points and Conditional Breakpoints
This effectively replaces the if statement on line 4 with the code in the eval
point.
About Interpreted and Compiled Expressions
On all platforms, TotalView can interpret your eval points. It can compile
them on HP Alpha Tru64 UNIX, IBM AIX, and SGI IRIX platforms. On HP
Alpha Tru64 UNIX and IBM AIX platforms, compiling the expressions in eval
points is the default.
If your platform supports compiled eval points, your performance will be
significantly better, particularly if your program is using multi-processors.
This is because interpreted eval points are single-threaded through the
TotalView process. In contrast, compiled eval points execute on each processor.
The TV::compile_expressions CLI variable enables or disables compiled
expressions. See “Operating Systems” in the TotalView Reference Guide for information
about how TotalView handles expressions on specific platforms.
Using any of the following functions forces TotalView to interpret the eval point rather
than compile it: $clid, $duid, $nid, $processduid, $systid, $tid, and $visualize.
In addition, $pid forces interpretation on IBM AIX.
About Interpreted Expressions
Interpreted expressions are interpreted by TotalView. Interpreted expressions
run slower, possibly much slower, than compiled expressions. With multiprocess
programs, interpreted expressions run even more slowly because
processes may need to wait for TotalView to execute the expression.
When you debug remote programs, interpreted expressions always run
slower because the TotalView process on the host, not the TotalView server
(tvdsvr) on the client, interprets the expression. For example, an interpreted
expression could require that 100 remote processes wait for the
TotalView process on the host machine to evaluate one interpreted expression.
In contrast, if TotalView compiles the expression, it evaluates them on
each remote process.
Whenever a thread hits an interpreted eval point, TotalView stops execution. This means
that TotalView creates a new set of lockstep groups. Consequently, if goal threads contain
interpreted patches, the results are unpredictable.
About Compiled Expressions
TotalView compiles, links, and patches expressions into the target process.
Because the target thread executes this code, eval points and conditional
breakpoints execute very quickly. (Conditional watchpoints are always
interpreted.) Also, this code doesn’t need to communicate with the
TotalView host process until it needs to.
370 Chapter 16: Setting Action Points