LBR callchains from tracepoints

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Apr 25, 2016 at 10:03:58PM -0300, Arnaldo Carvalho de Melo escreveu:
> I now need to continue investigation why this doesn't seem to work from
> tracepoints...

Bummer, the changeset (at the end of this message) hasn't any
explanation, is this really impossible? I.e. LBR callstacks from
tracepoints? Even if we set perf_event_attr.exclude_callchain_kernel?

I've read somewhere that LBR wouldn't work for the kernel, but when I
tried, for cycles:ppp I got:

[acme@jouet linux]$ perf record --call-graph lbr usleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.018 MB perf.data (9 samples) ]
[acme@jouet linux]$ perf evlist -v
cycles:ppp: size: 112, { sample_period, sample_freq }: 4000,
sample_type: IP|TID|TIME|CALLCHAIN|PERIOD|BRANCH_STACK, disabled: 1,
inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1,
precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec:
1, branch_sample_type: USER|CALL_STACK|NO_FLAGS|NO_CYCLES
[acme@jouet linux]$

-   59.69%  usleep   [kernel]  [k] vma_interval_tree_insert
    →vma_interval_tree_insert  [kernel]
     vma_adjust                [kernel]
     __split_vma.isra.31       [kernel]
     split_vma                 [kernel]
     mprotect_fixup            [kernel]
     sys_mprotect              [kernel]
     entry_SYSCALL_64_fastpath [kernel]
     mprotect                  ld-2.22.so
     _dl_relocate_object       ld-2.22.so
     memcpy@GLIBC_2.2.5        libc-2.22.so
     _dl_relocate_object       ld-2.22.so
     __gettimeofday            libc-2.22.so
     _dl_vdso_vsym             libc-2.22.so
     _dl_lookup_symbol_x       ld-2.22.so

This was done on a Broadwell system (ThinkPad t450s).

- Arnaldo

commit 2481c5fa6db0237e4f0168f88913178b2b495b7c
Author: Stephane Eranian <eranian@google.com>
Date:   Thu Feb 9 23:20:59 2012 +0100

    perf: Disable PERF_SAMPLE_BRANCH_* when not supported
    
    PERF_SAMPLE_BRANCH_* is disabled for:
    
     - SW events (sw counters, tracepoints)
     - HW breakpoints
     - ALL but Intel x86 architecture
     - AMD64 processors
    
    Signed-off-by: Stephane Eranian <eranian@google.com>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/1328826068-11713-10-git-send-email-eranian@google.com
    Signed-off-by: Ingo Molnar <mingo@elte.hu>