Em Wed, Feb 12, 2020 at 12:13:46PM +0100, Jiri Olsa escreveu: > On Tue, Feb 11, 2020 at 04:32:23PM -0300, Arnaldo Carvalho de Melo wrote: > > Historically vmlinux was preferred because it contains function sizes, > > but with all these out of the blue symbols, we need to prefer starting > > with /proc/kallsyms and, as we do now, continue getting updates via > > PERF_RECORD_KSYMBOL. > > Humm, but then trampolines don't generate that, right? Or does it? If it > > doesn't, then we will know about just the trampolines in place when the > > record/top session starts, reparsing /proc/kallsyms periodically seems > > excessive? > I plan to extend the KSYMBOL interface to contain trampolines/dispatcher > data, That seems like the sensible, without looking too much at all the details, to do, yes. > plus we could do some inteligent fallback to /proc/kallsyms in case > vmlinux won't have anything At this point what would be the good reason to prefer vmlinux instead of going straight to using /proc/kallsyms? We have support for taking a snapshot of it at 'perf top' start, i.e. right at the point we need to resolve a kernel symbol, then we get PERF_RECORD_KSYMBOL for things that gets in place after that. And as well we save it to the build-id cache so that later, at 'perf report/script' time we can resolve kernel symbols, etc. vmlinux is just what is in there right before boot, after that, for quite some time, _lots_ of stuff happens :-) - Arnaldo
