linux-kernel - Re: [PATCH] perf tools: set no branch type for dummy event in PT

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Date:   Thu, 29 Jun 2017 17:29:12 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     kan.liang@...el.com
Cc:     acme@...nel.org, linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, adrian.hunter@...el.com,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com
Subject: Re: [PATCH] perf tools: set no branch type for dummy event in PT

On Wed, Jun 28, 2017 at 10:31:53AM -0400, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> An earlier kernel patch allowed enabling PT and LBR at the same
> time on Goldmont. 
> commit ccbebba4c6bf ("perf/x86/intel/pt: Bypass PT vs. LBR
> exclusivity if the core supports it")
> However, users still cannot use Intel PT and LBRs simultaneously.
>     $ sudo perf record -e cycles,intel_pt//u -b  -- sleep 1
>     Error:
>     PMU Hardware doesn't support sampling/overflow-interrupts.
> 
> PT implicitly adds dummy event in perf tool. dummy event is
> software event which doesn't support LBR.
> 
> Always setting branch_type=no for dummy event in Intel PT.
> 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  tools/perf/arch/x86/util/intel-pt.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/tools/perf/arch/x86/util/intel-pt.c b/tools/perf/arch/x86/util/intel-pt.c
> index f630de0..651ab9e 100644
> --- a/tools/perf/arch/x86/util/intel-pt.c
> +++ b/tools/perf/arch/x86/util/intel-pt.c
> @@ -544,6 +544,22 @@ static int intel_pt_validate_config(struct perf_pmu *intel_pt_pmu,
>  					evsel->attr.config);
>  }
>  
> +static int add_no_lbr_config_term(struct list_head *config_terms)
> +{
> +	struct perf_evsel_config_term *lbr_term;
> +
> +	lbr_term = zalloc(sizeof(*lbr_term));
> +	if (!lbr_term)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&lbr_term->list);
> +	lbr_term->type = PERF_EVSEL__CONFIG_TERM_BRANCH;
> +	lbr_term->val.branch = strdup("no");
> +	list_add_tail(&lbr_term->list, config_terms);
> +
> +	return 0;
> +}
> +
>  static int intel_pt_recording_options(struct auxtrace_record *itr,
>  				      struct perf_evlist *evlist,
>  				      struct record_opts *opts)
> @@ -701,6 +717,8 @@ static int intel_pt_recording_options(struct auxtrace_record *itr,
>  				perf_evsel__set_sample_bit(switch_evsel, TIME);
>  				perf_evsel__set_sample_bit(switch_evsel, CPU);
>  
> +				add_no_lbr_config_term(&switch_evsel->config_terms);
> +

hum, why can't you change the sample bit directly? with:

			perf_evsel__reset_sample_bit(switch_evsel, BRANCH_STACK);

jirka