Re: profilers

Chris F Clark <>
12 Dec 1997 14:47:39 -0500

          From comp.compilers

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Re: profilers (Chris F Clark) (1997-12-12)
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| List of all articles for this month |

From: Chris F Clark <>
Newsgroups: comp.compilers
Date: 12 Dec 1997 14:47:39 -0500
Organization: The World Public Access UNIX, Brookline, MA
References: 97-12-017 97-12-046 97-12-063
Keywords: performance, testing

"William A. Barath" <> wrote a description of a
profiling scheme where a high precision counter was subtracted between
profiling points to which the moderator responded:
>[That's what Unix C compilers do with the -p flag. -John]
to which Fergus Henderson replied:
> Are you sure? I thought Unix C compilers inserted profiling code that
> recorded execution *counts* for each function, but that for doing the
> actual timing they used PC-sampling techiques based on the use of
> `setitimer(ITIMER_PROF, ...)' to schedule regular `SIGPROF' signals.

Fergus, both you and the moderator are right. The normal profiling
done on Unix systems is statistical. However, some Unix profiling
tools, such as DEC's Atom, can do the timing based upon high
resolution counters and subtracting the difference. Also don't
neglect tools like Pixie which statically count (or otherwise
simulate) the instructions and then only need number of times each
instruction sequence (basic block) is executed--although that can
neglect factors like cache misses caused by other processes.


Chris Clark Internet :
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3 Proctor Street voice : (508) 435-5016
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