On Tue, Oct 07, 2014 at 02:59:20AM +0000, Liang, Kan wrote: > > 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++;
Yes, that avoids the ctx->task_ctx_data deref when !branch_user_callstack(). -- 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/
