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Date: Wed, 24 Sep 2014 14:53:49 +0200 From: Peter Zijlstra <peterz@...radead.org> To: kan.liang@...el.com Cc: eranian@...gle.com, linux-kernel@...r.kernel.org, mingo@...hat.com, paulus@...ba.org, acme@...nel.org, ak@...ux.intel.com, "Yan, Zheng" <zheng.z.yan@...el.com> Subject: Re: [PATCH V5 08/16] perf, x86: track number of events that use LBR callstack On Wed, Sep 10, 2014 at 10:09:05AM -0400, kan.liang@...el.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? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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