From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ionut Georgescu Date: Fri, 24 Oct 2003 16:26:55 +0000 Subject: Re: Itanium2@900MHz slower than alpha@666MHz ? Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org Yes, it is a 1.5MB cache CPU. But it might be more than just cache misses. When running with a 256x256 grid, I am actually using 3 256x257 matrices, which is slightly over 1.5MB. I just made a comparison with a 32x32 grid and the difference is the same: alpha 10.294s, zx2000 14.777s . -O3 is only by 0.4s faster than -O2 in this case. The variations are within +-0.02s between runs (for the 32x32 case). Is there a way to test the bandwidth of the cache ? Because I think the alphas have actually 2MB of L2 cache, not L3. Thanks, Ionut On Fri, Oct 24, 2003 at 04:35:43PM +0100, Matthew Wilcox wrote: > On Fri, Oct 24, 2003 at 05:14:50PM +0200, Ionut Georgescu wrote: > > I am puzzled about the speed of a zx2000 workstation with a 900Mhz CPU. > > According to the SPECfp2000 benchmarks, this workstation should be about > > twice as fast as a DS10 alpha workstation and according to the fftw2 > > benchmarks at least 50% faster (double precision, real data, 256x256 FFT > > transforms). I ran the fftw2 benchmark myself and I could reproduce the > > data on fftw.org > > > > However, my program is about 40% slower on the zx2000 as on the alpha. > > It only does some Fourier transforms (fftw2, 256x256) and some matrix > > operations (sort of an inner product). Both fftw2 and the program have > > been compiled with ecc -O2 -ipo -limf. ecc is Version 7.1, Build > > 20030307. > > This strikes me as possibly being a cache size thing. Do you have the > 1.5MB cache or 3MB cache version of the 900MHz Itanium? The DS10 specs > I found at > http://www.spec.org/cpu2000/results/res2000q3/cpu2000-20000630-00134.asc > say it has a 2MB cache, so if your data set fits in a 2MB cache and not > in a 1.5MB cache, that would be a possible cause. > > What kind of fluctuations do you see between runs? Linux doesn't > do cache-colouring, so high variation between runs could indicate a > close-to-edge-of-cache scenario. > > -- > "It's not Hollywood. War is real, war is primarily not about defeat or > victory, it is about death. I've seen thousands and thousands of dead bodies. > Do you think I want to have an academic debate on this subject?" -- Robert Fisk > -- *************** * Ionut Georgescu * http://www.physik.tu-cottbus.de/~george/ * Registered Linux User #244479 * * "In Windows you can do everything Microsoft wants you to do; in Unix you * can do anything the computer is able to do."