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

[Like Xu]

Hi Joe,

On 2019/7/18 13:18, Joe Perches wrote:
> 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.

The spamming case in practice from this messages is very rare but it's 
logically possible.

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

Thanks and it's my mistake, agree on '\n' usage.

> 		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@xxxxxxxxxx >>