Joakim, Enable loop unrolling by default for 8xx processors is not a good idea because of the limited instructions cache size.
I think that's also what is recommended in the ppc faq: enable size optimization (-Os) for 8xx processors gives better performance. For a 750 or so, it would be good to enable loop unrolling. Jaap-Jan > > Hi > > I optimized the crc32() in JFFS2(fs/jffs2/crc.h) by manually unrolling > the crc32 loop. This gave me a speed increase of 22% in mounting JFFS2 FS > > Later Alan Cox pointed out that my changes makes x86 run slower and it turns > out that on x86 and a fairly new gcc will automatically unroll loops 'where > appropriate' > > Removed my hand coded unrolling and added -funroll-loops to the JFFS2 > Makefile, > I got similar results as my hand coded unrolling (a little better). > > I therefore conclude that ppc_8xx-gcc 2.95.3 from Monta Vista does not do ANY > unrolling > unless you specify -funroll-loops. Doing this for the whole kernel is NOT a > good idea, > it will run slower due to big increase of size. > > Now I wonder: > Is this a gcc 2.95.3, PPC or Monta Vista limitation? > > Which compiler will do unrolling 'where appropriate' for 8xx PPC and > Where can I get a precompiled version? > > The short term solution is to specify -funroll-loops for individual > files/directories. > Obviously JFFS2 should be included, but what else? > > > > ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/