On Wed, Oct 2, 2013 at 9:08 AM, Jan Hubicka <hubi...@ucw.cz> wrote: >> > Hi, >> > >> > >> > >> > Current default probability for builtin_expect is 0.9996. >> > This makes the freq of unlikely bb very low (4), which >> > suppresses the inlining of any calls within those bb. >> > >> > We used FDO data to measure the branch probably for >> > the branch annotated with builtin_expert. >> > For google internal benchmarks, the weight average >> > (the profile count value as the weight) is 0.9081. >> > >> > Linux kernel is another program that is heavily annotated >> > with builtin-expert. We measured its weight average as 0.8717, >> > using google search as the workload. >> > >> > This patch sets the alternate hirate probability for builtin_expert >> > to 90%. With the alternate hirate, we measured performance >> > improvement for google benchmarks and Linux kernel. >> > >> > An earlier discussion is >> > https://mail.google.com/mail/u/0/?pli=1#label/gcc-paches/1415c5910054630b >> > >> > This new patch is for the trunk and addresses Honza's comments. >> > >> > Honza: this new probability is off by default. When we backport to google >> > branch we will make it the default. Let me know if you want to do the same >> > here. > > I do not like much the binary parameter for > builtin-expect-probability-relaxed. > > I would just add bulitin-expect-probability taking value in percents and then > make predict.c to use it. Just use predict_edge instead of predict_edge_def > and document hitrate value as unused in predict.def.
Thanks for the suggestion. This is much cleaner than to use binary parameter. Just want to make sure I understand it correctly about the orginal hitrate: you want to retire the hitrate in PRED_BUILTIN_EXPECT and always use the one specified in the biniltin-expect-probability parameter. Should I use 90% as the default? It's hard to fit current value 0.9996 in percent form. -Rong > > OK with that change. > > Honza
