linux-kernel - Re: [PATCH] kvm: no need to check return value of debugfs

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Message-ID: <d7b38792-e91f-be0c-20cf-99023962f0a9@redhat.com>
Date:   Wed, 23 Jan 2019 00:11:18 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christian Borntraeger <borntraeger@...ibm.com>
Cc:     linux-kernel@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org
Subject: Re: [PATCH] kvm: no need to check return value of debugfs_create
 functions

On 22/01/19 21:48, Greg Kroah-Hartman wrote:
>> This also brings the question: shall we move these counters out of debugfs into something else?
> If you have code that relies on debugfs, yes, you need to move that out
> of debugfs because more and more systems are trying to disable it due to
> the obvious problems with it (i.e. leaking tons of debugging
> information).
> 
> debugfs is for DEBUG information, not for "statistics about how my VM is
> working".  That sounds like something you need to rely on, so debugfs is
> not the place for it.

Yes, we know that and tracepoints are already one replacement.  However,
they are slower that just a lock-free "vcpu->stats.foo_happened++".
Another idea that Steven Rostedt and I discussed a while ago is some
kind of "statfs" which would already provide some code, similar to the
one that KVM uses to accumulate statistics from multiple VMs or multiple
VCPUs into a single counter.

Paolo