From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <3CDAB8FC.D833842C@esteem.com> Date: Thu, 09 May 2002 10:59:24 -0700 From: Conn Clark MIME-Version: 1.0 To: linuxppc-embedded@lists.linuxppc.org Subject: Performance on PPC8xx using string and multiple load instructions? (finalized) Content-Type: text/plain; charset=us-ascii Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: Hello, Does anyone know how using the -mstring and -mmultiple GCC code optimization switches affect performance on the PPC8xx ? The book I have on PPC assembly says the use of the string and load-multiple instrutions may be signifigantly slower than the multiple instruction equivalent on some processors. It does not tell me which processors or why. I think it might be due to ther fact that multiple instructions can be paired in multi instruction pipelined chips. Since the 8xx has only a sigle pipeline I was wondering if this was the case. In the kernel source they use the -mmultiple and -mstring switches in the PPC architecture dependant code. This may have been done to reduce code size or it was done with the impression that it would make things faster as I first thought before looking into it. I also discovered (according to GCC documentation) that these instructions don't work on most processors in Little-Endian Mode (not that it gets used much). If these instructions are signifigantly slower on some processors and won't work on most in Little-Endian Mode is this a good idea to have them as default optimizations for all processors? Unfortunatly I only have access to our proprietary MPC850 board and have little experience in benchmarking. If anybody ever benchmarked code with and with out these instructions on an 8xx processor or other processor I would like to see the results. Thanks in advance Conn -- ***************************************************************** If you live at home long enough, your parents will move out. ***************************************************************** Conn Clark Engineering Stooge clark@esteem.com Electronic Systems Technology Inc. www.esteem.com ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/