From: Paolo Bonzini <pbonzini@redhat.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Jing Zhang <jingzhangos@google.com>, KVM <kvm@vger.kernel.org>,
KVM ARM <kvmarm@lists.cs.columbia.edu>,
Linux MIPS <linux-mips@vger.kernel.org>,
KVM PPC <kvm-ppc@vger.kernel.org>,
Linux S390 <linux-s390@vger.kernel.org>,
Linux kselftest <linux-kselftest@vger.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>
Subject: Re: [RFC PATCH 3/4] KVM: stats: Add ioctl commands to pull statistics in binary format
Date: Wed, 10 Mar 2021 18:44:27 +0100 [thread overview]
Message-ID: <fd37d21f-f3ae-d370-f8e1-cf552be3b2ee@redhat.com> (raw)
In-Reply-To: <871rcmhq43.wl-maz@kernel.org>
On 10/03/21 18:31, Marc Zyngier wrote:
>> Maintaining VM-global counters would require an atomic instruction and
>> would suffer lots of cacheline bouncing even on architectures that
>> have relaxed atomic memory operations.
> Which is why we have per-cpu counters already. Making use of them
> doesn't seem that outlandish.
But you wouldn't be able to guarantee consistency anyway, would you?
You *could* copy N*M counters to userspace, but there's no guarantee
that they are consistent, neither within a single vCPU nor within a
single counter.
>> Speed/efficiency of retrieving statistics is important, but let's keep
>> in mind that the baseline for comparison is hundreds of syscalls and
>> filesystem lookups.
>
> Having that baseline in the cover letter would be a good start, as
> well as an indication of the frequency this is used at.
Can't disagree, especially on the latter which I have no idea about.
Paolo
next prev parent reply other threads:[~2021-03-10 17:45 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-10 0:30 [RFC PATCH 0/4] KVM: stats: Retrieve statistics data in binary format Jing Zhang
2021-03-10 0:30 ` [RFC PATCH 1/4] KVM: stats: Separate statistics name strings from debugfs code Jing Zhang
2021-03-10 14:19 ` Marc Zyngier
2021-03-10 18:51 ` Jing Zhang
2021-03-10 0:30 ` [RFC PATCH 2/4] KVM: stats: Define APIs for aggregated stats retrieval in binary format Jing Zhang
2021-03-10 14:58 ` Marc Zyngier
2021-03-10 19:36 ` Jing Zhang
2021-03-10 0:30 ` [RFC PATCH 3/4] KVM: stats: Add ioctl commands to pull statistics " Jing Zhang
2021-03-10 14:55 ` Paolo Bonzini
2021-03-10 21:41 ` Jing Zhang
2021-03-12 18:11 ` Paolo Bonzini
2021-03-12 22:27 ` Jing Zhang
2021-03-13 9:35 ` Paolo Bonzini
2021-03-15 22:31 ` Jing Zhang
2021-03-16 17:54 ` Paolo Bonzini
2021-03-10 15:51 ` Marc Zyngier
2021-03-10 16:03 ` Paolo Bonzini
2021-03-10 17:05 ` Marc Zyngier
2021-03-10 17:11 ` Paolo Bonzini
2021-03-10 17:31 ` Marc Zyngier
2021-03-10 17:44 ` Paolo Bonzini [this message]
2021-03-10 21:43 ` Jing Zhang
2021-03-10 0:30 ` [RFC PATCH 4/4] KVM: selftests: Add selftest for KVM binary form statistics interface Jing Zhang
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