linux-kernel - Re: [PATCH] KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed

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Message-ID: <9eda0e29f524275a217411ea81352271b782baa4.camel@perches.com>
Date:   Wed, 17 Jul 2019 22:18:46 -0700
From:   Joe Perches <joe@...ches.com>
To:     Like Xu <like.xu@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Avi Kivity <avi@...lladb.com>
Cc:     kvm@...r.kernel.org, Gleb Natapov <gleb@...hat.com>,
        like.xu@...ux.inetl.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/vPMU: refine kvm_pmu err msg when event
 creation failed

On Thu, 2019-07-18 at 12:49 +0800, Like Xu wrote:
> If a perf_event creation fails due to any reason of the host perf
> subsystem, it has no chance to log the corresponding event for guest
> which may cause abnormal sampling data in guest result. In debug mode,
> this message helps to understand the state of vPMC and we should not
> limit the number of occurrences.
[]
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
[]
> @@ -131,8 +131,8 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
>  						 intr ? kvm_perf_overflow_intr :
>  						 kvm_perf_overflow, pmc);
>  	if (IS_ERR(event)) {
> -		printk_once("kvm_pmu: event creation failed %ld\n",
> -			    PTR_ERR(event));
> +		pr_debug("kvm_pmu: event creation failed %ld\n for pmc->idx = %d",
> +			    PTR_ERR(event), pmc->idx);

Perhaps this was written as printk_once to avoid
spamming the log with repeated messages.

Maybe this should use pr_debug_ratelimited.
(and it should also have a \n termination like:)

		pr_debug_ratelimited("kvm_pmu: event creation failed %ld for pmc->idx = %d\n",
				     PTR_ERR(event), pmc->idx);

Perhaps Avi Kivity remembers why he wrote it this way.
https://lore.kernel.org/kvm/1305129333-7456-6-git-send-email-avi@redhat.com/