Messages in this thread | | | Date | Wed, 24 Sep 2014 14:53:49 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V5 08/16] perf, x86: track number of events that use LBR callstack |
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On Wed, Sep 10, 2014 at 10:09:05AM -0400, kan.liang@intel.com wrote: > @@ -204,9 +204,15 @@ void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in) > } > } > > +static inline bool branch_user_callstack(unsigned br_sel) > +{ > + return (br_sel & X86_BR_USER) && (br_sel & X86_BR_CALL_STACK); > +} > + > void intel_pmu_lbr_enable(struct perf_event *event) > { > struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events); > + struct x86_perf_task_context *task_ctx; > > if (!x86_pmu.lbr_nr) > return; > @@ -220,6 +226,10 @@ void intel_pmu_lbr_enable(struct perf_event *event) > } > cpuc->br_sel = event->hw.branch_reg.reg; > > + task_ctx = event->ctx ? event->ctx->task_ctx_data : NULL; > + if (task_ctx && branch_user_callstack(cpuc->br_sel)) > + task_ctx->lbr_callstack_users++; > +
Does it make sense to flip those conditions to avoid a potentially useless dereference?
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