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Re: AutoFDO profile toolchain is open-sourced
- From: Ilya Palachev <i dot palachev at samsung dot com>
- To: Diego Novillo <dnovillo at google dot com>
- Cc: GCC Development <gcc at gcc dot gnu dot org>, David Li <davidxl at google dot com>, Jan Hubicka <hubicka at ucw dot cz>, Sebastian Pop <sebpop at gmail dot com>, Dehao Chen <dehao at google dot com>, Vyacheslav Barinov <v dot barinov at samsung dot com>
- Date: Tue, 21 Apr 2015 16:42:34 +0300
- Subject: Re: AutoFDO profile toolchain is open-sourced
- Authentication-results: sourceware.org; auth=none
- References: <CAO2gOZWydpiBXb=1QDyCRt-ybDieqy8X4S_+uRZk2Y2v+cFdYQ at mail dot gmail dot com> <5523ED98 dot 8080007 at samsung dot com> <CAFk3UF8To5Qcz8NN5rUF3z6j8CCg_89A+62P=1U9YrtbZ5=mLg at mail dot gmail dot com> <20150410203927 dot GA18980 at atrey dot karlin dot mff dot cuni dot cz> <552E1613 dot 2040405 at samsung dot com> <5536278E dot 3090706 at samsung dot com> <CAD_=9DQEqCqzyBKT8nZ1_uEt5gU589hSpLiOHUqLXKctJTaVHA at mail dot gmail dot com>
On 21.04.2015 14:57, Diego Novillo wrote:
>From the autofdo page: https://github.com/google/autofdo
[ ... ]
--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-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
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?