linux-kernel - [PATCHv2 1/1] perf/x86/intel: make error messages less confusing

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Date:   Thu, 23 Aug 2018 08:07:32 -0700
From:   Eduardo Valentin <eduval@...zon.com>
To:     Andi Kleen <ak@...ux.intel.com>
CC:     Eduardo Valentin <eduval@...zon.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Kan Liang" <kan.liang@...ux.intel.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Jia Zhang <qianyue.zj@...baba-inc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCHv2 1/1] perf/x86/intel: make error messages less confusing

On a system with X86_FEATURE_ARCH_PERFMON disabled
and with a model not known by family PMU drivers,
user gets a kernel message log like the following:
[ 0.100114] Performance Events: unsupported p6 CPU model 85 no PMU driver, software events only.

The "unsupported .. CPU" part may be confusing for some
users leading to wrong understanding that the kernel
does not support the CPU model.

This patch rewords the messages on the failure path to:
[ 0.667154] Performance Events: CPU does not support PMU: no PMU driver, software events only.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Kan Liang <kan.liang@...ux.intel.com>
Cc: Dan Carpenter <dan.carpenter@...cle.com>
Cc: Eduardo Valentin <eduval@...zon.com>
Cc: Jia Zhang <qianyue.zj@...baba-inc.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Eduardo Valentin <eduval@...zon.com>
---

Changes from V1->V2:
- As per initial review, the propose messaging was even
more confusing. Simplified it by only saying that
the CPU does not support PMU.


 arch/x86/events/intel/core.c | 15 +++++++++++----
 arch/x86/events/intel/p4.c   |  5 +----
 arch/x86/events/intel/p6.c   |  1 -
 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 035c37481f57..2ddb97f03f4a 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3889,15 +3889,22 @@ __init int intel_pmu_init(void)
 	char *name;
 
 	if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
+		int ret = -ENODEV;
+
 		switch (boot_cpu_data.x86) {
 		case 0x6:
-			return p6_pmu_init();
+			ret = p6_pmu_init();
+			break;
 		case 0xb:
-			return knc_pmu_init();
+			ret = knc_pmu_init();
+			break;
 		case 0xf:
-			return p4_pmu_init();
+			ret = p4_pmu_init();
+			break;
 		}
-		return -ENODEV;
+		if (ret)
+			pr_cont("CPU does not support PMU: ");
+		return ret;
 	}
 
 	/*
diff --git a/arch/x86/events/intel/p4.c b/arch/x86/events/intel/p4.c
index d32c0eed38ca..fb5e8576d9ac 100644
--- a/arch/x86/events/intel/p4.c
+++ b/arch/x86/events/intel/p4.c
@@ -1345,11 +1345,8 @@ __init int p4_pmu_init(void)
 	BUILD_BUG_ON(ARCH_P4_MAX_CCCR > INTEL_PMC_MAX_GENERIC);
 
 	rdmsr(MSR_IA32_MISC_ENABLE, low, high);
-	if (!(low & (1 << 7))) {
-		pr_cont("unsupported Netburst CPU model %d ",
-			boot_cpu_data.x86_model);
+	if (!(low & (1 << 7)))
 		return -ENODEV;
-	}
 
 	memcpy(hw_cache_event_ids, p4_hw_cache_event_ids,
 		sizeof(hw_cache_event_ids));
diff --git a/arch/x86/events/intel/p6.c b/arch/x86/events/intel/p6.c
index 408879b0c0d4..e8e03e68b22f 100644
--- a/arch/x86/events/intel/p6.c
+++ b/arch/x86/events/intel/p6.c
@@ -269,7 +269,6 @@ __init int p6_pmu_init(void)
 		break;
 
 	default:
-		pr_cont("unsupported p6 CPU model %d ", boot_cpu_data.x86_model);
 		return -ENODEV;
 	}
 
-- 
2.18.0