Profiler Speed

[Bill Baxter]

On Fri, Jan 16, 2009 at 9:44 AM, Christopher Wright <dhasenan at gmail.com> wrote:
> bearophile wrote:
>>
>> Nick Sabalausky:
>>>
>>> Isn't that kind of a common thing with profilers in general?
>>
>> Any physical measure alters the thing to be measured, but with a good
>> enough brain you can generally invent ways to decrease such alteration to
>> tolerable levels. So it's a matter of inventing better solutions.
>>
>> There are many kinds of profilers, some of them work "outside" with a
>> random probing of a program, while it runs. I think such kind of profiler
>> may slow down your code as little as you want (but the less it sample the
>> less precise is the result).
>
> Additionally, you can turn profiling on and off with most profilers, so you
> only get a 3-4x slowdown until you start profiling (at which point it's more
> like 20x, judging by ANTS profiler for C#).

Right, that would probably do the trick, except I don't think there's
anyway to programatically turn D's profiler on or off.  So if you've
got a program with a big startup cost and you want to profile
something that happens after startup, it means you could be waiting a
long time to get to the thing you actually care about, and by that
time the profile logs are filled up with a bunch of unrelated junk.

So I think your only hope with the D profile is to try to extract out
the chunk you want to profile into a separate program.  Not always
possible, and often when possible only painfully so.

--bb