Mailing-List: contact cygwin-help AT sourceware DOT cygnus DOT com; run by ezmlm List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner AT sources DOT redhat DOT com Delivered-To: mailing list cygwin AT sources DOT redhat DOT com From: tprinceusa AT mindspring DOT com Date: Fri, 10 Nov 2000 19:33:34 -0500 To: McNulty Junior Bobby Cc: cygwin AT sources DOT redhat DOT com Subject: Re: 8 bit alignnment Message-ID: X-Originating-IP: 134.134.248.28 Yes, the performance of cygwin-compiled code using 64-bit data (C double, Fortran double precision,..) is abysmal with the standard 32-bit or 4 byte alignment. I have been running for some time with binutils rebuilt for 64-bit alignment. The results with gcc and g77 are excellent (doesn't even interfere with rebuilding gcc), but it breaks important parts of the existing g++ and objc run-time support binaries. I suppose that I have introduced struct/class padding mis-match. I'm hoping to try rebuilding the libraries to see if that will cure this. The .p2align code and long double data alignments used by the gcc aren't fully effective without 128-bit alignment, which doesn't appear to be possible with cygwin. Going from 32-bit to 64-bit alignment does, I believe, greatly reduce the number of incidents where .p2align hurts rather than helping. With the change to 64-bit alignment, cygwin/gcc out-performs some big name Windows C++ and linux gcc compilers on certain tests of the effect of alignment on memory bandwidth. And the big name Windows compilers cheat a bit with their 8-byte long doubles. Yes, binutils, combined with the cygwin run-time, keep the stack aligned to the selected boundaries. The stack is supposed to be 128-bit aligned in linux with the current glibc. In principle, you could make a function which would set the stack up to your selected alignment each time you call it. Not a good practice in general. This alignment thing has been around at least 30 years, and it's not going away, with the greater use of 64-bit architectures. McNulty Junior Bobby wrote: > Have you guys thought of compiling the code with 8 bit alignments? This will bring Cygwin to 64 bits. I know. I did this with Csound, and it is acting better. I read how to optimize the programs that I use and the alignment was one of them. Actually, i think it was the stack boundary. -- Want to unsubscribe from this list? Send a message to cygwin-unsubscribe AT sourceware DOT cygnus DOT com