> > On Wed, Sep 10, 2014 at 10:09:05AM -0400, [email protected] 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?
I'm not quite sure I understand your meaning here. But lbr_callstack_users is an indicator for save/restore the LBR stack on context switch. Here, we only change the lbr_callstack_users, when it's LBR call stack and has space for saving LBR stack. Should I change the code as below? + if (branch_user_callstack(cpuc->br_sel) && event->ctx && + (task_ctx = event->ctx->task_ctx_data)) + task_ctx->lbr_callstack_users++; Kan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
