On Mon, 2008-09-01 at 09:23 +0200, David Jander wrote: > On Friday 29 August 2008 14:20:33 Joakim Tjernlund wrote: > >[...] > > > The problem is: I have very little experience with powerpc assembly and > > > only very limited time to dedicate to this and I am looking for others > > > who have > > > > I improved the PowerPC memcpy and friends in uClibc a while ago. It does > > basically the same a the kernel memcpy but without any cache > > instructions. It is written in C, but in such a way that > > optimal assembly is generated. > > Hmm, isn't that going to break on a different version of gcc?
Not break, but gcc might generate non optimal code. However, the code is laid out to make it easy for gcc to do the right thing. > I just copied the latest version of trunk/uClibc/libc/string/powerpc/memcpy.c > from subversion as uclibc-memcpy.c, removed the last line and did this: > > $ gcc -shared -O2 -Wall -o libucmemcpy.so uclibc-memcpy.c > > (should I use other compiler options?) These are fine. > > Then I started my test program with LD_PRELOAD=... > > My test program only copies big chunks of aligned memory, so it will only > test > for maximum throughput (such as copying video frames). I will make a better > one, to measure throughput on different sized blocks of aligned and unaligned > memory, but first I want to find out why I can't seem to get even close to > the expected RAM bandwidth (bursts occur at 1.6 Gbyte/s, sustained transfers > might be able to reach 400 Mbyte/s in theory, taking into account the video > controller eating almost half of it, I'd like to get somewhere close to 200). > > The result is quite a bit better than that of glibc-2.7 (13.2 Mbyte/s --> 22 > Mbyte/s), but still far from the 71.5 Mbyte/s achieved when using bigger > strides of 16 registers load/store at a time. > Note, that this is copy performance, one-way througput should be double these > figures. Yeah, the code is trying to do a reasonable job without knowing what micro arch it is running on. These could probably go to glibc as new general purpose memxxx() routines. You will probably see a big increase once dcbz is added to the copy/memset functions. Fire away :) Jocke _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
