[naviserver-devel] Profiling

[David O. <da...@qc...>]

Hi,

We've been looking at profiling the execution times of various
application-level procs running NaviServer.

We want the ability to turn on profiling for selected commands, so we
started off using Tcl traces in a manner similar to:
http://nikit.tcl.tk/page/Profiling+with+execution+traces

So we'd have a proc to set up a Tcl trace on command execution enter/leave
in a list like so:

proc instrument {args} {
    #| Takes list of commands and adds Tcl execution trace for entering and
exit
    set script ""
    foreach cmd $args {
            append script "trace add execution $cmd enter profile_begin\n"
            append script "trace add execution $cmd leave profile_end\n"
        }
    }
    eval $script
}


At the start of each proc in the list we'd push the start time to a stack:

proc profile_begin args {
    # Append current time to timer stack for this thread
    variable ::timerStack
    lappend ::timerStack [::tcl::clock::microseconds]
}

And then pop off the time when proc exits:

proc profile_end {command_string code result op} {
    #| Pop value off timer stack for this thread and record a subsegment
    variable ::timerStack
    set start_time [lindex $::timerStack end]
    set end_time [::tcl::clock::microseconds]
    set ::timerStack [lrange $::timerStack 0 end-1]
    record_the_timing $command_string $start_time $end_time
}


It wasn't obvious to me how to set up these Tcl traces so they are active
in each NaviServer interpreter, but after some trial and error, I could get
a result by using ns_ictl to set up a callback on interpreter allocation
and use that to set up the Tcl trace:

ns_ictl trace allocate "instrument $cmd_list"

This seems to work ok but has the disadvantage that I think I need to
restart NaviServer in order to add or remove commands.

So I wanted to ask:
1. Is there a more dynamic way of setting up Tcl traces across NaviServer
interpreters?
2. Is anyone aware of a different/better way of profiling applications
running under NaviServer?

Regards,
-- 
David