linuxlinux-kernelprofilingperf

Perf: kernel module symbols not showing up in profiling

On loading and running a kernel module and then profiling through perf.

$ perf record -a -g --call-graph dwarf sleep 30
$ perf report

my kernel module's symbols are not present in the perf's report. Although the symbols are present in /proc/kallsyms. Also the module is not present in perf buildid-list As this answer says to make the module a kernel module, I tried but didn't help. What are the possible reasons that could lead to this?

Solution

  • The message Failed to open [thrUserCtrl], continuing without symbols sounds like perf was unable to find your module. Try installing it into 

    /lib/modules/`uname -r`/extra

    directory as said in https://wiki.centos.org/HowTos/BuildingKernelModules:

    6. In this example, the file cifs.ko has just been created. 
 As root, copy the .ko file to the /lib/modules/<kernel-version>/extra/
 directory.

       [root@host linux-2.6.18.i686]# cp fs/cifs/cifs.ko /lib/modules/`uname -r`/extra

    (don't forget depmod -a command after changing files in /lib/modules)

    This message is generated in map__load: http://elixir.free-electrons.com/linux/v4.11/source/tools/perf/util/map.c#L284

    int map__load(struct map *map)
{
    const char *name = map->dso->long_name;
    int nr;
    ...
    nr = dso__load(map->dso, map);
    if (nr < 0) {
        if (map->dso->has_build_id) {
         ...
        } else
            pr_warning("Failed to open %s", name);

        pr_warning(", continuing without symbols\n");
        return -1;

    when dso__load function returns error.