pprof + "redis-server --loadmodule ./build/libmymodule.so"

[Zongheng Yang]

Hi all,

Has anyone tried using pprof [0] to profile a redis-server, loaded with a custom module?

Here's how I launched the binary:

     $ CPUPROFILE=/tmp/prof.out redis/src/redis-server --loadmodule ./build/libmymodule.so

After this is set up, I launched commands, and shut down the server.  Then,

     $ ~/bin/pprof -tree redis/src/redis-server /tmp/prof.out

*does* print out the analyzed profile, but without any symbols, an except is here (https://pastebin.com/EUtzdfAm):

    flat  flat%   sum%        cum   cum%   calls calls% + context

----------------------------------------------------------+-------------

                                             1.80s 39.91% |   <unknown>

                                             1.16s 25.72% |   [libtcmalloc.4.dylib]

                                             0.59s 13.08% |   [libmember.so]

                                             0.40s  8.87% |   [redis-server]

                                             0.23s  5.10% |   [libprofiler.0.dylib]

                                             0.21s  4.66% |   [libc++.1.dylib]

     4.51s 92.61% 92.61%      4.51s 92.61%                | [libsystem_kernel.dylib]

where libmember.so is my custom module.  The libmember.so library is built in the following way:

  set(REDIS_MODULE_CFLAGS -W -Wall -dynamic -fno-common -g -ggdb -std=c++11 -O2)

  set(REDIS_MODULE_LDFLAGS "-undefined dynamic_lookup")

  set(CMAKE_SHARED_LIBRARY_SUFFIX ".so")

  add_library(member SHARED member.cc)

  target_compile_options(member PUBLIC ${REDIS_MODULE_CFLAGS} -fPIC)

  target_link_libraries(member profiler)

  target_link_libraries(member tcmalloc)

My question: how do I change the compilation / linking, so that symbolization works?

[0] https://github.com/gperftools/gperftools

Thanks,

Zongheng

[Dvir Volk]

Hi.

A few things to try:

1. Try --add_lib=/path/to/your/lib.so

2. If that doesn't work, try stating your module and not redis-server as the executable. 

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[Zongheng Yang]

Hi Dvir,

Do you mean to supply --add_lib to "pprof", or to "redis-server"?

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[Dvir Volk]

To pprof. If you module is linked with -lprofiler and you object files are compiled with -g -ggdb is works.

I did however have to add explicit calls in my C code to start profiling, it didn't generate anything meaningful if I didn't.

[Zongheng Yang]

I'm using this version of pprof (https://github.com/google/pprof), and it doesn't have an --add_lib argument.

I also tried adding ProfilerStart(..) in my custom module; same issue.

One thing to check though: you said "my C code", was your setup the same as mine (launch redis-server with a custom_module.so)?  Did you have to compile antirez/redis differently (I just did `make`, no other options)? 

[Zongheng Yang]

Dvir,

If you were using the same or sufficiently similar setup, it'd be great if you can paste your workflow.  Thanks! 

[Dvir Volk]

Same as yours. -lprofiler on the linker, redis compiled normally, my module compiled with debug symbols CPUPROFILE set, nothing else.

[Zongheng Yang]

Thanks.  I did not get this to work on Mac, but succeeded on an Ubuntu box.