Re: [PATCH V6 13/17] perf, x86: enable LBR callstack when recording callchain

Jiri Olsa
2014-10-24T13:39:50Z

On Sun, Oct 19, 2014 at 05:55:08PM -0400, Kan Liang wrote:
> Only enable LBR callstack when user requires fp callgraph. The feature
> is not available when PERF_SAMPLE_BRANCH_STACK or PERF_SAMPLE_STACK_USER
> is required.
> Also, this feature only affects how to get user callchain. The kernel
> callchain is always got by frame pointers.
>
> Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
> Signed-off-by: Kan Liang <kan.liang@intel.com>
> ---
> arch/x86/kernel/cpu/perf_event.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 9656b9e..b3256a3 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -424,10 +424,24 @@ int x86_pmu_hw_config(struct perf_event *event)
> if (!event->attr.exclude_kernel)
> *br_type |= PERF_SAMPLE_BRANCH_KERNEL;
> }
> - }
> + } else if (x86_pmu_has_lbr_callstack() &&
> + (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) &&
> + !(event->attr.sample_type & PERF_SAMPLE_STACK_USER) &&
> + !has_branch_stack(event) &&
> + !event->attr.exclude_user &&
> + (event->attach_state & PERF_ATTACH_TASK)) {
> + /*
> + * user did not specify branch_sample_type,
> + * try using the LBR call stack facility to
> + * record call chains of user program.
> + */
> + event->attr.branch_sample_type =
> + PERF_SAMPLE_BRANCH_USER |
> + PERF_SAMPLE_BRANCH_CALL_STACK;
>

I dont see PERF_SAMPLE_BRANCH_CALL_STACK being defind in uapi.. any reason
why I cant enable this feature explicitly?

thanks,
jirka