Richard Henderson writes: > On Tue, Feb 15, 2005 at 05:27:15PM +0000, Andrew Haley wrote: > > So, now for my question: why do we not call __register_frame_info() or > > __register_frame_info_bases() ? > > Because in the normal case for C/C++, folks don't use that many > exceptions. So delaying doing anything until it's needed is a win. > > Obviously the normal case is different for Java.
Yeah. In the big server application I'm working on, almost 40% of total CPU time is spent inside one function, _Unwind_IteratePhdrCallback(). This is for a few reasons: firstly, java uses stack traces for things other than throwing exceptions. Exceptions are relatively rare. Also, in a big server application you have a lot of shared libraries: this one has 86. So, for every single stack frame we're doing many excursions through _Unwind_IteratePhdrCallback(). > > We'd avoid a great many trips through > > dl_iterate_phdr () and _Unwind_IteratePhdrCallback(). > > While I still like using dl_iterate_phdr instead of > __register_frame_info_bases for totally aesthetic reasons, there > have been changes made to the dl_iterate_phdr interface since the > gcc support was written that would allow the dl_iterate_phdr > results to be cached. That would be nice. Also, we could fairly easily build a tree of nodes, one for each loaded object, then we wouldn't be doing a linear search through them. We could do that lazily, so it wouldn't kick in 'til needed. Andrew.
