linux-kernel - Re: [PATCH 3.16 47/47] KVM: x86/vPMU: refine kvm

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Date:   Sat, 2 Nov 2019 03:39:30 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Ben Hutchings <ben@...adent.org.uk>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        Like Xu <like.xu@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 3.16 47/47] KVM: x86/vPMU: refine kvm_pmu err msg when
 event creation failed

On Fri, Nov 01, 2019 at 08:40:23AM -0700, Joe Perches wrote:
>On Fri, 2019-11-01 at 04:07 -0400, Sasha Levin wrote:
>> On Thu, Oct 31, 2019 at 03:53:23PM -0700, Joe Perches wrote:
>> > On Thu, 2019-10-31 at 22:14 +0000, Ben Hutchings wrote:
>> > > On Fri, 2019-10-25 at 12:05 -0700, Joe Perches wrote:
>> > > > On Fri, 2019-10-25 at 19:03 +0100, Ben Hutchings wrote:
>> > > > > 3.16.76-rc1 review patch.  If anyone has any objections, please let me know.
>> > > >
>> > > > This seems more like an enhancement than a bug fix.
>> > > >
>> > > > Is this really the type of patch that is appropriate
>> > > > for stable?
>> > >
>> > > Apparently so:
>> > >
>> > > v4.14.135: eba797dbf352 KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
>> > > v4.19.61: ba27a25df6df KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
>> > > v4.4.187: 505c011f9f53 KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
>> > > v4.9.187: 3984eae04473 KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
>> > > v5.1.20: edadec197fbf KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
>> > > v5.2.3: 9f062aef7356 KVM: x86/vPMU: refine kvm_pmu err msg when event creation failed
>> >
>> > I think not, but hey, maybe you and Greg do.
>> >
>> > Porting enhancements, even trivial ones, imo is
>> > not a great thing for stable branches.
>> >
>> > My perspective is that only bug fixes should be
>> > applied to stable branches.
>>
>> Usability issues are just as bad as code bugs. Our human interface is at
>> least as important as the functionality of our code.
>
>Umm.
>
>#define DEBUG is not set here.
>
>Changing from printk_once to pr_debug_ratelimited completely
>eliminates the output from non CONFIG_DYNAMIC_DEBUG configs,
>and this output message is not enabled by default either.

Maybe I'm missing something, but Paolo explained why: it was a useless
debug feature because it used to print once early on but not when it's
actually needed. Now it's actually useful for users who want to debug
but it won't flood regular users who are not inteterested in it.

-- 
Thanks,
Sasha