(j3.2006) More on "contiguous"

[keith bierman]

On May 15, 2007, at 3:02 PM, Van Snyder wrote:

> g line 312, gprof is telling

gprof can be horribly, horribly wrong. Unless it's changed in the  
years since I last looked (which seems doubtful unix people tend to  
create new profilers not alter the zen nature of the old ones) it has  
a clock granularity of 1/100th of a second, which happens to also be  
the timer for a ton of system activities. I used to have some lecture  
notes (from how to use the tools that I used to give lectures from)  
where I had examples of gprof completely misallocating time from one  
procedure to a completely different one in the call tree.

Depending on your platform, you may have some more advanced profiling  
engines (some allow you to actually time code segments, others allow  
you to choose smaller or larger time quanta for sampling than the  
system timer ... either, both are useful. if you get consistent  
results irrespective of the quantum size perhaps it's real. if it  
varies a lot, chances are you've got something naster than your tool  
is able to handle going on).
> ///ment and the next one is
> an IF statement, I assume the reported time is all spent at this line.
Or something else in the call tree (especially if the optimizer has  
created routines out of loops, or things which appear so to gprof  
(outlining, the obverse of inlining for example, or calling a  
"memset" routine on your behalf for the special case of setting a  
constant)

>

Keith H. Bierman    keith.bierman at Sun.COM   |  khbkhb at gmail.com
Sun Microsystems Microelectronics Group     | sun IM: khb AIM: kbiermank
5430 Nassau Circle East                     | 650-352-4432 voice+fax
Cherry Hills Village, CO 80113              | sun internal 68207
http://blogs.sun.com/khb                    | 303-997-2749
<speaking for myself, not Sun*> Copyright 2007



Keith H. Bierman    keith.bierman at Sun.COM   |  khbkhb at gmail.com
Sun Microsystems Microelectronics Group     |
5430 Nassau Circle East                     | 650-352-4432 voice+fax
Cherry Hills Village, CO 80113              | sun internal 68207
http://blogs.sun.com/khb                    | 303-997-2749
<speaking for myself, not Sun*> Copyright 2007

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