On Tue, Apr 21, 2015 at 6:42 AM, Ilya Palachev <i.palac...@samsung.com> wrote: > On 21.04.2015 14:57, Diego Novillo wrote: >> >> >From the autofdo page: https://github.com/google/autofdo >> >> [ ... ] >> Inputs: >> >> --profile: PERF_PROFILE collected using linux perf (with last branch >> record). >> In order to collect this profile, you will need to have an Intel CPU that >> have last branch record (LBR) support. You also need to have your linux >> kernel configured with LBR support. To profile: >> # perf record -c PERIOD -e EVENT -b -o perf.data -- ./command >> EVENT is refering to BR_INST_RETIRED:TAKEN if available. For some >> architectures, BR_INST_EXEC:TAKEN also works. >> [ ... ] >> >> The important one for autofdo is -b. It asks perf to use LBR registers >> for branch tracking (assuming your architecture supports it). > > > Thanks! It worked. Now big programs produce big gcov files. Sorry for this > confusing message. > > But why create_gcov does not inform about that (no branch events were > found)? It creates empty gcov file and says nothing :( > > Moreover, in the mentioned README it is said that perf should also be > executed with option -e BR_INST_RETIRED:TAKEN. > I tried to add it but perf said that > > invalid or unsupported event: 'BR_INST_RETIRED:TAKEN' > Run 'perf list' for a list of valid events > > For my architecture x86_64 the perf list contains > > $ sudo perf list | grep -i br > branch-instructions OR branches [Hardware event] > branch-misses [Hardware event] > branch-loads [Hardware > cache event] > branch-load-misses [Hardware > cache event] > branch-instructions OR cpu/branch-instructions/ [Kernel PMU event] > branch-misses OR cpu/branch-misses/ [Kernel PMU event] > mem:<addr>[:access] [Hardware breakpoint] > syscalls:sys_enter_brk [Tracepoint event] > syscalls:sys_exit_brk [Tracepoint event] > > There is no BR_INST_RETIRED:TAKEN there. Do you use some specific > configuration of perf for that? > > However, I tried to use option "-e branch-instructions". Before that the > following error was obtained: > > E0421 15:57:39.308374 11551 perf_parser.cc:210] Mapped 50% of > samples, expected at least 95% > > and now it disappeared (because of option "-e branch-instructions"). > > Though, the performance decreases after adding option > "-fauto-profile=file.gcov" or "-fprofile-use=file.gcov" to the list of > compiler options. > The program becomes 10% slower than before. > Can you explain that? Maybe I should configure perf so that it will be able > to collect events BR_INST_RETIRED:TAKEN ? How can it be done?
You can use dump_gcov to show a text version of the profile dump and check if the profile data makes sense. If your program is just a very tight single loop, the current implementation in trunk may not yield good results because it does not have discriminator support. Try the google-4_9 branch instead. Dehao > > > -- > Best regards, > Ilya Palachev
