Cc'ing Rong since he is also working on trying to address the comdat profile issue. Rong, you may need to see an earlier message for more context: http://gcc.gnu.org/ml/gcc-patches/2013-08/msg00558.html
Teresa On Sun, Aug 11, 2013 at 5:21 AM, Jan Hubicka <hubi...@ucw.cz> wrote: >> >> I see, yes LTO can deal with this better since it has global >> information. In non-LTO mode (including LIPO) we have the issue. > > Either Martin or me will implement merging of the multiple copies at > LTO link time. This is needed for Martin's code unification patch anyway. > > Theoretically gcov runtime can also have symbol names and cfg checksums of > comdats in the static data and at exit produce buckets based on matching > names+checksums+counter counts, merge all data into in each bucket to one > representative by the existing merging routines and then memcpy them to > all the oriignal copiles. This way all compilation units will receive same > results. > > I am not very keen about making gcov runtime bigger and more complex than it > needs to be, but having sane profile for comdats seems quite important. > Perhaps, in GNU toolchain, ordered subsections can be used to make linker to > produce ordered list of comdats, so the runtime won't need to do hashing + > lookups. > > Honza >> >> I take it gimp is built with LTO and therefore shouldn't be hitting >> this comdat issue? >> >> Let me do a couple things: >> - port over my comdat inlining fix from the google branch to trunk and >> send it for review. If you or Martin could try it to see if it helps >> with function splitting to avoid the hits from the cold code that >> would be great >> - I'll add some new sanity checking to try to detect non-zero blocks >> in the cold section, or 0 blocks reached by non-zero edges and see if >> I can flush out any problems with my tests or a profiledbootstrap or >> gimp. >> - I'll try building and profiling gimp myself to see if I can >> reproduce the issue with code executing out of the cold section. >> >> Thanks, >> Teresa >> >> >> >> >> Also, can you send me reproduction instructions for gimp? I don't >> >> think I need Martin's patch, but which version of gimp and what is the >> >> equivalent way for me to train it? I have some scripts to generate a >> >> similar type of instruction heat map graph that I have been using to >> >> tune partitioning and function reordering. Essentially it uses linux >> >> perf to sample on instructions_retired and then munge the data in >> >> several ways to produce various stats and graphs. One thing that has >> >> been useful has been to combine the perf data with nm output to >> >> determine which cold functions are being executed at runtime. >> > >> > Martin? >> > >> >> >> >> However, for this to tell me which split cold bbs are being executed I >> >> need to use a patch that Sri sent for review several months back that >> >> gives the split cold section its own name: >> >> http://gcc.gnu.org/ml/gcc-patches/2013-04/msg01571.html >> >> Steven had some follow up comments that Sri hasn't had a chance to >> >> address yet: >> >> http://gcc.gnu.org/ml/gcc-patches/2013-05/msg00798.html >> >> (cc'ing Sri as we should probably revive this patch soon to address >> >> gdb and other issues with detecting split functions properly) >> > >> > Intresting, I used linker script for this purposes, but that his GNU ld >> > only... >> > >> > Honza >> >> >> >> Thanks! >> >> Teresa >> >> >> >> > >> >> > Honza >> >> >> >> >> >> Thanks, >> >> >> Teresa >> >> >> >> >> >> > I think we are really looking primarily for dead parts of the >> >> >> > functions (sanity checks/error handling) >> >> >> > that should not be visited by train run. We can then see how to >> >> >> > make the heuristic more aggressive? >> >> >> > >> >> >> > Honza >> >> >> >> >> >> >> >> >> >> >> >> -- >> >> >> Teresa Johnson | Software Engineer | tejohn...@google.com | >> >> >> 408-460-2413 >> >> >> >> >> >> >> >> -- >> >> Teresa Johnson | Software Engineer | tejohn...@google.com | 408-460-2413 >> >> >> >> -- >> Teresa Johnson | Software Engineer | tejohn...@google.com | 408-460-2413 -- Teresa Johnson | Software Engineer | tejohn...@google.com | 408-460-2413
