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/
