On Thu, Feb 14, 2019 at 6:00 AM Arnaldo Carvalho de Melo <[email protected]> wrote: > > Em Thu, Feb 14, 2019 at 02:26:38PM +0100, Jiri Olsa escreveu: > > On Thu, Feb 14, 2019 at 09:57:59AM -0300, Arnaldo Carvalho de Melo wrote: > > > But with the build id in the MMAPs we wouldn't need to scan anything at > > > 'perf record' time, just at 'perf archive' time, where we would scan > > > everything, and as soon as we find a hit, we add that DSO to the list of > > > things we need to put in the tarball. > > > ok.. it might little change the expected behavour in that you will not > > have .debug cache populated until you run perf archive.. some profile > > data might stop report after you reinstall the binary.. > Today perf record does collect the buildids once monitor is completed, it does one pass over the perf.data file looking for MMAP records, or at least in the version I am more familiar with.
> Well, nothing prevents us from continuing to, in 'perf record', go thru > the perf.data just collected to populate the .debug cache, its just that > we would do it just for that, for populating the cache, we wouldn't > _have_ to do that for collecting the buildids. Sure, for compatibility reasons. In pipe mode, this would also avoid the need for perf inject -b -i -, which is a win. perf archive is useful if you do not have a way to locate the binary using only the buildid on the analysis machine. > > > on the other hand '.debug' cache would stop growing uncontrolably.. > > so I think I'd be ok with this > I agree! > That is another problem, and one that has to be solved in a way similar > to ccache's --max-size option. > > The .debug cache is useful for various workflows, but may get in the way > for some others, which is why we have ways to disable it. > Correct. > For instance, when working on some project it is handy to have copies of > binaries saved so that older perf.data files can find a file that was > rewritten by the compiler when doing changes in it, etc. > > With the .debug cache and if using -g, we can get the older copy of the > binary _and_ its sources, annotation for older versions continue to > work, etc. > > - Arnaldo
