linux-kernel - [PATCH 1/1] perf/x86: Use KERN_INFO when checking PMU fails on virtual environment

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Message-Id: <1411617314-24659-1-git-send-email-wei@redhat.com>
Date:	Wed, 24 Sep 2014 22:55:14 -0500
From:	Wei Huang <wei@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, Wei Huang <wei@...hat.com>
Subject: [PATCH 1/1] perf/x86: Use KERN_INFO when checking PMU fails on virtual environment

PMU checking can fail due to various reasons. On native machine,
this is mostly caused by faulty hardware and it is reasonable to
use KERN_ERR in reporting. However, when kernel is running on
virtualized environment, this checking can fail if virtual PMU is
not supported (e.g. KVM on AMD host). It is annoying to see
an error message on splash screen, even though we know such failure
is benign on virtualized environment.

This patch checks if kernel is running in virtualized environment.
If so, it will use KERN_INFO in reporting. This patch was tested
successfully on KVM.

Signed-off-by: Wei Huang <wei@...hat.com>
---
 arch/x86/kernel/cpu/perf_event.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 918d75f..16c7302 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -243,7 +243,8 @@ static bool check_hw_exists(void)
 
 msr_fail:
 	printk(KERN_CONT "Broken PMU hardware detected, using software events only.\n");
-	printk(KERN_ERR "Failed to access perfctr msr (MSR %x is %Lx)\n", reg, val_new);
+	printk(boot_cpu_has(X86_FEATURE_HYPERVISOR) ? KERN_INFO : KERN_ERR
+	       "Failed to access perfctr msr (MSR %x is %Lx)\n", reg, val_new);
 
 	return false;
 }
-- 
1.9.3

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