I have an Intel D845GE m/b w/ a P4 1.7 CPU and I have the box setup to dual boot
to either 4.9 or 5.2. Both OS are right off the latest posted iso CD image, i.e., no updates,
no kernel tweaks, everything vanilla right out of the box. I compiled flops.c on both 4.9
and 5.2 and the 5.2 performance is less than half that of 4.9: 760 MFLOPS on 4.9 v/s
340 MFLOPS on 5.2.
I tried turning off the SMP and other kernel tweaks and no improvement in 5.2. I then
downloaded and installed gcc295 on the 5.2 machine and that fixed the problem. So
now all I have to do is figure out the gcc 3.3.3 switches to make it run like gcc 2.9.5 or
figure out how to rebuild 5.2 w/ gcc 2.9.5 :-).
Anyone know what's going on w/ gcc 3.3.3 ?
%gcc295 flops.c -o flops %./flops
FLOPS C Program (Double Precision)
Version 1.2, 29 Feb 1992PI: Program = 3.14159265358999429 PI: Reference = 3.14159265358979312 PI: Error = 2.0117e-13
Area: Program = 0.50000000000008060 Area: Reference = 0.50000000000000000 Area: Error = 8.0602e-14
Iterations = 20000000 BenchTime(usec) = 0.0013 Scalar MFLOPS = 760.2353
%gcc flops.c -o flops %./flops
FLOPS C Program (Double Precision)
Version 1.2, 29 Feb 1992PI: Program = 3.14159265358999429 PI: Reference = 3.14159265358979312 PI: Error = 2.0117e-13
Area: Program = 0.50000000000008060 Area: Reference = 0.50000000000000000 Area: Error = 8.0602e-14
Iterations = 20000000 BenchTime(usec) = 0.0029 Scalar MFLOPS = 339.4571
%
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