We already were able to ask for callchains for a specific event:

  # trace -e nanosleep --call dwarf --event sched:sched_switch/call-graph=fp/ usleep 1

This would enable tracing just the "nanosleep" syscall, with callchains
at syscall exit and would ask the kernel for frame pointer callchains to
be enabled for the "sched:sched_switch" tracepoint event, its just that
we were not resolving the callchain and printing it in 'perf trace', do
it:

  # trace -e nanosleep --call dwarf --event sched:sched_switch/call-graph=fp/ usleep 1
     0.425 ( 0.013 ms): usleep/6718 nanosleep(rqtp: 0x7ffcc1d16e20) ...
     0.425 (         ): sched:sched_switch:usleep:6718 [120] S ==> swapper/2:0 [120])
                                       __schedule+0xfe200402 ([kernel.kallsyms])
                                       schedule+0xfe200035 ([kernel.kallsyms])
                                       do_nanosleep+0xfe20006f ([kernel.kallsyms])
                                       hrtimer_nanosleep+0xfe2000dc ([kernel.kallsyms])
                                       sys_nanosleep+0xfe20007a ([kernel.kallsyms])
                                       do_syscall_64+0xfe200062 ([kernel.kallsyms])
                                       return_from_SYSCALL_64+0xfe200000 ([kernel.kallsyms])
                                       __nanosleep+0xffff008b8cbe2010 (/usr/lib64/libc-2.22.so)
     0.486 ( 0.073 ms): usleep/6718  ... [continued]: nanosleep()) = 0
                                       __nanosleep+0x10 (/usr/lib64/libc-2.22.so)
                                       usleep+0x34 (/usr/lib64/libc-2.22.so)
                                       main+0x1eb (/usr/bin/usleep)
                                       __libc_start_main+0xf0 (/usr/lib64/libc-2.22.so)
                                       _start+0x29 (/usr/bin/usleep)
  #

Pretty compact, huh? DWARF callchains for raw_syscalls:sys_exit + frame
pointer callchains for a tracepoint, if your hardware supports LBR, go
wild with /call-graph=lbr/, guess the next step is to lift this from
'perf script':

  -F, --fields <str>    comma separated output fields prepend with 'type:'. Valid types: hw,sw,trace,raw.
                        Fields: comm,tid,pid,time,cpu,event,trace,ip,sym,dso,addr,symoff,period,iregs,brstack,brstacksym,flags

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-2e7yiv5hqdm8jywlmfivvx2v@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>