Anthony Green writes: > On Tue, 2005-06-07 at 16:38 -0400, Andrew Overholt wrote: > > Hi, > > > > I've spent a bit of time doing some more $subj. These reports (and > > samples) were taken with --no-vmlinux. Please tell me if there's something > > else I should be doing. > > I recently checked in a change to the GCC 4.0 branch that saves over 10k > exceptions and related memory allocations during Eclipse startup. > > This change appeared in today's gcc-4.0.0-11. Is this what you're > using? It seems the profile is spending much of its time inside the exception unwinder. This might be due to the fact that Eclipse uses a huge number of shared libraries, enough to blow out the cache. To explain: in libgcc we have a cache used for unwinding. The cache tells us which shared library contains the PC. Whenever we look up a PC value, we look in the cache. Each cache element contains pc_low and pc_high. There are 8 cache entries, which is sufficient in almost all cases. However, Eclipse has a huge number of libraries, and I suspect the cache is being flushed every time. The reason I suspect this is the large number of calls to search_object(). It is also possible that there is some problem with unwinder data. This will cause a linear search to be done instead of a binary search. > Also, are you using FC4's oprofile, or the one from oprofile cvs? > > See > https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=157854 > > Your profiles look a little bit like the bogus ones I reported. I think so. I don't believe 8% of total time inside __do_global_ctors_aux. Also, search_object() is being called a huge number of times but none of the routines that it calls appear in the profile. This is impossible. Andrew. static const fde * search_object (struct object* ob, void *pc) { /* If the data hasn't been sorted, try to do this now. We may have more memory available than last time we tried. */ if (! ob->s.b.sorted) { init_object (ob); /* Despite the above comment, the normal reason to get here is that we've not processed this object before. A quick range check is in order. */ if (pc < ob->pc_begin) return NULL; } if (ob->s.b.sorted) { if (ob->s.b.mixed_encoding) return binary_search_mixed_encoding_fdes (ob, pc); else if (ob->s.b.encoding == DW_EH_PE_absptr) return binary_search_unencoded_fdes (ob, pc); else return binary_search_single_encoding_fdes (ob, pc); } else { /* Long slow labourious linear search, cos we've no memory. */ if (ob->s.b.from_array) { fde **p; for (p = ob->u.array; *p ; p++) { const fde *f = linear_search_fdes (ob, *p, pc); if (f) return f; } return NULL; } else return linear_search_fdes (ob, ob->u.single, pc); } }
