Re: [PATCH] kvm: no need to check return value of debugfs_create functions

From: Paolo Bonzini <pbonzini@redhat.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>
Cc: linux-kernel@vger.kernel.org, "Radim Krčmář" <rkrcmar@redhat.com>,
	kvm@vger.kernel.org
Subject: Re: [PATCH] kvm: no need to check return value of debugfs_create functions
Date: Wed, 23 Jan 2019 00:11:18 +0100	[thread overview]
Message-ID: <d7b38792-e91f-be0c-20cf-99023962f0a9@redhat.com> (raw)
In-Reply-To: <20190122204828.GA30805@kroah.com>

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