Messages in this thread | ![/](/images/icornerl.gif) | | From | Denis Vlasenko <> | Subject | Re: gcc 2.95 vs 3.21 performance | Date | Tue, 4 Feb 2003 08:54:41 +0200 |
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On 4 February 2003 01:31, Richard B. Johnson wrote: > On Mon, 3 Feb 2003, Martin J. Bligh wrote: > > People keep extolling the virtues of gcc 3.2 to me, which I'm > > reluctant to switch to, since it compiles so much slower. But > > it supposedly generates better code, so I thought I'd compile > > the kernel with both and compare the results. This is gcc 2.95 > > and 3.2.1 from debian unstable on a 16-way NUMA-Q. The kernbench > > tests still use 2.95 for the compile-time stuff. > > [SNIPPED tests...]
What was the size of uncompressed kernel binaries? This is a simple (and somewhat inaccurate) measure of compiler improvement ;)
> Don't let this get out, but egcs-2.91.66 compiled FFT code > works about 50 percent of the speed of whatever M$ uses for > Visual C++ Version 6.0 I was awfully disheartened when I
Yes. M$ (and some other compilers) beat GCC badly.
> found that identical code executed twice as fast on M$ than > it does on Linux. I tried to isolate what was causing the > difference. So I replaced 'hypot()' with some 'C' code that > does sqrt(x^2 + y^2) just to see if it was the 'C' library. > It didn't help. When I find out what type (section) of code > is running slower, I'll report. In the meantime, it's fast > enough, but I don't like being beat by M$.
I'm afraid it's code generation engine. It is just worse than M$ or Intel's one. It is not easily fixable, GCC folks have tremendous task at hand.
I wonder whether some big companies supposedly supporting Linux (e.g. Intel) can help GCC team (for example by giving away some code and/or developer time). -- vda - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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