Re: [PATCH v9 0/5] KVM statistics data fd-based binary interface

From: Leon Romanovsky <leon@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Jing Zhang <jingzhangos@google.com>, KVM <kvm@vger.kernel.org>,
	KVMARM <kvmarm@lists.cs.columbia.edu>,
	LinuxMIPS <linux-mips@vger.kernel.org>,
	KVMPPC <kvm-ppc@vger.kernel.org>,
	LinuxS390 <linux-s390@vger.kernel.org>,
	Linuxkselftest <linux-kselftest@vger.kernel.org>,
	Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Will Deacon <will@kernel.org>,
	Huacai Chen <chenhuacai@kernel.org>,
	Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Paul Mackerras <paulus@ozlabs.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	David Hildenbrand <david@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Jim Mattson <jmattson@google.com>,
	Peter Shier <pshier@google.com>, Oliver Upton <oupton@google.com>,
	David Rientjes <rientjes@google.com>,
	Emanuele Giuseppe Esposito <eesposit@redhat.com>,
	David Matlack <dmatlack@google.com>,
	Ricardo Koller <ricarkol@google.com>,
	Krish Sadhukhan <krish.sadhukhan@oracle.com>,
	Fuad Tabba <tabba@google.com>
Subject: Re: [PATCH v9 0/5] KVM statistics data fd-based binary interface
Date: Tue, 15 Jun 2021 16:34:05 +0300	[thread overview]
Message-ID: <YMisTWKdyNgPvdQV@unreal> (raw)
In-Reply-To: <9df462c0-e0ea-8173-0705-369d6a81107c@redhat.com>

On Tue, Jun 15, 2021 at 01:03:34PM +0200, Paolo Bonzini wrote:
> On 15/06/21 09:53, Leon Romanovsky wrote:
> > > Sorry for my naive questions, but how does telemetry get statistics
> > > for hypervisors? Why is KVM different from hypervisors or NIC's statistics
> > > or any other high speed devices (RDMA) that generate tons of data?
> > 
> > So the answer to the question "why KVM is different" is that it doesn't
> > have any stable identification except file descriptor. While hypervisors
> > have stable names, NICs and RDMA devices have interface indexes etc.
> > Did I get it right?
> 
> Right.
> 
> > And this was second part of my question, the first part was my attempt to
> > get on answer why current statistics like process info (/proc/xxx/*), NICs
> > (netlink) and RDMA (sysfs) are not using binary format.
> 
> NICs are using binary format (partly in struct ethtool_stats, partly in an
> array of u64).  For KVM we decided to put the schema and the stats in the
> same file (though you can use pread to get only the stats) to have a single
> interface and avoid ioctls, unlike having both ETH_GSTRINGS and ETH_GSTATS.
> 
> I wouldn't say processes are using any specific format.  There's a mix of
> "one value per file" (e.g. cpuset), human-readable tabular format (e.g.
> limits, sched), human- and machine-readable tabular format (e.g. status),
> and files that are ASCII but not human-readable (e.g. stat).

I see, your explanation to Enrico cleared the mud.

Thanks

> 
> Paolo
> 