On Thu, May 17, 2018 at 12:49:58PM +0200, Christophe Leroy wrote: > In my 8xx configuration, I get 208 calls to memcmp() > Within those 208 calls, about half of them have constant sizes, > 46 have a size of 8, 17 have a size of 16, only a few have a > size over 16. Other fixed sizes are mostly 4, 6 and 10. > > This patch inlines calls to memcmp() when size > is constant and lower than or equal to 16 > > In my 8xx configuration, this reduces the number of calls > to memcmp() from 208 to 123 > > The following table shows the number of TB timeticks to perform > a constant size memcmp() before and after the patch depending on > the size > > Before After Improvement > 01: 7577 5682 25% > 02: 41668 5682 86% > 03: 51137 13258 74% > 04: 45455 5682 87% > 05: 58713 13258 77% > 06: 58712 13258 77% > 07: 68183 20834 70% > 08: 56819 15153 73% > 09: 70077 28411 60% > 10: 70077 28411 60% > 11: 79546 35986 55% > 12: 68182 28411 58% > 13: 81440 35986 55% > 14: 81440 39774 51% > 15: 94697 43562 54% > 16: 79546 37881 52%
Could you show results with a more recent GCC? What version was this? What is this really measuring? I doubt it takes 7577 (or 5682) timebase ticks to do a 1-byte memcmp, which is just 3 instructions after all. Segher
