From: "Jürgen Strobel" <strobel@...>
Date: 2006-08-29T11:35:30+09:00
Subject: Re: For performance, write it in C

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On Sat, Aug 26, 2006 at 11:23:02PM +0900, Jordan Callicoat wrote:
> J=FCrgen Strobel wrote:

> Ok, fair enough. I made the assumption that the testing was done on a=20
> terminal emulator since the perl execution time was given as 12 minutes=
=20
> and the faster version of the ruby algorithm writing to a file rather=20
> than stdout took only 17 seconds, whereas it took 26 minutes writing to=
=20
> stdout--I assumed that the perl version would be comparable with file=20
> writing rather than writing to standard out. I used xterm.
>=20
> > All you did benchmark was that your terminal emulator (or whereever
> > your stdout goes to) is slow.
>=20
> Yes! That's exactly what I was trying to do! I was trying to show that=20
> writing to stdout (assuming a comparable context, like an xterm) is the=
=20
> bottle-neck of the ruby version here. Writing to a file was about 90=20
> times faster. Like I said, I wasn't denying that C is faster; my point=20
> was this: the C version may only take 5 seconds to write to a *file*,=20
> but ruby only takes 17 seconds; and for me, as I'm sure for others, 12=20
> seconds is not worth the effort of writing it in C. So the 12 minutes to=
=20
> 5 seconds comparison was flawed -- 17 seconds to 5 seconds is more=20
> accurate.

Usually you don't benchmark with external arbitrary bottlenecks
enabled. The point is, *your* xterm may be of very different speed
than mine. Generic terminal emulators are not a comparable context at
all, not without benchmarking them themselves, which is not the point
of this exercise.

I should have emphasized *your terminal emulator*. We are comparing
ruby vs. C, so it makes sense to assume a fast and uniform output
mechanism which doesn't get in our way. It is standard practice to
write to stdout, but redirect it to /dev/null or files if writeing
larger quantities in benchmarks.

To get real numbers, your C version took 0.010s CPU time, and your
ruby one took 0.202s. A difference of roughly 2000% may well be
important to several applications. Sometimes it may be completely
irrelevant, for instance if CPU time is dwarfed by I/O.

-J=FCrgen

--=20
 The box said it requires Windows 95 or better so I installed Linux

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