linux-kernel - Re: [PATCH V5 04/25] perf/x86/intel: Hybrid PMU support for perf capabilities

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Date:   Thu, 8 Apr 2021 13:40:41 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
        tglx@...utronix.de, bp@...en8.de, namhyung@...nel.org,
        jolsa@...hat.com, ak@...ux.intel.com, yao.jin@...ux.intel.com,
        alexander.shishkin@...ux.intel.com, adrian.hunter@...el.com,
        ricardo.neri-calderon@...ux.intel.com
Subject: Re: [PATCH V5 04/25] perf/x86/intel: Hybrid PMU support for perf
 capabilities



On 4/8/2021 1:00 PM, Peter Zijlstra wrote:
> On Mon, Apr 05, 2021 at 08:10:46AM -0700, kan.liang@...ux.intel.com wrote:
>> +#define is_hybrid()			(!!x86_pmu.num_hybrid_pmus)
> 
> Given this is sprinkled all over the place, can you make this a
> static_key_false + static_branch_unlikely() such that the hybrid case is
> out-of-line?
> 

Sure, I will add a new static_key_false "perf_is_hybrid" to indicate a 
hybrid system as below (not test yet).

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index f8d1222..bd6412e 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -54,6 +54,7 @@ DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = {

  DEFINE_STATIC_KEY_FALSE(rdpmc_never_available_key);
  DEFINE_STATIC_KEY_FALSE(rdpmc_always_available_key);
+DEFINE_STATIC_KEY_FALSE(perf_is_hybrid);

  /*
   * This here uses DEFINE_STATIC_CALL_NULL() to get a static_call defined
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 2b553d9..7cef3cd 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -6119,6 +6119,7 @@ __init int intel_pmu_init(void)
  					     GFP_KERNEL);
  		if (!x86_pmu.hybrid_pmu)
  			return -ENOMEM;
+		static_branch_enable(&perf_is_hybrid);
  		x86_pmu.num_hybrid_pmus = X86_HYBRID_NUM_PMUS;

  		x86_pmu.late_ack = true;
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index bfbecde..d6383d1 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -663,8 +663,8 @@ static __always_inline struct x86_hybrid_pmu 
*hybrid_pmu(struct pmu *pmu)
  	return container_of(pmu, struct x86_hybrid_pmu, pmu);
  }

-/* The number of hybrid PMUs implies whether it's a hybrid system */
-#define is_hybrid()			(!!x86_pmu.num_hybrid_pmus)
+extern struct static_key_false perf_is_hybrid;
+#define is_hybrid()		static_branch_unlikely(&perf_is_hybrid)

  #define hybrid(_pmu, _field)				\
  ({							\

Thanks,
Kan