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From: Marc Zyngier <maz@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>
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 17:05:01 +0000	[thread overview]
Message-ID: <8735x3x7lu.wl-maz@kernel.org> (raw)
In-Reply-To: <a475d935-e404-93dd-4c6d-a5f8038d8f4d@redhat.com>

On Wed, 10 Mar 2021 16:03:42 +0000,
Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> On 10/03/21 16:51, Marc Zyngier wrote:
> >> +	kvm_for_each_vcpu(j, vcpu, kvm) {
> >> +		pdata = data + VM_STAT_COUNT;
> >> +		for (i = 0; i < VCPU_STAT_COUNT; i++, pdata++)
> >> +			*pdata += *((u64 *)&vcpu->stat + i);
> > Do you really need the in-kernel copy? Why not directly organise the
> > data structures in a way that would allow a bulk copy using
> > copy_to_user()?
> 
> The result is built by summing per-vCPU counters, so that the counter
> updates are fast and do not require a lock.  So consistency basically
> cannot be guaranteed.

Sure, but I wonder whether there is scope for VM-global counters to be
maintained in parallel with per-vCPU counters if speed/efficiency is
of the essence (and this seems to be how it is sold in the cover
letter).

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: KVM <kvm@vger.kernel.org>, David Hildenbrand <david@redhat.com>,
	Paul Mackerras <paulus@ozlabs.org>,
	Linux kselftest <linux-kselftest@vger.kernel.org>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Will Deacon <will@kernel.org>,
	KVM ARM <kvmarm@lists.cs.columbia.edu>,
	Emanuele Giuseppe Esposito <eesposit@redhat.com>,
	Linux S390 <linux-s390@vger.kernel.org>,
	Janosch Frank <frankja@linux.ibm.com>,
	Oliver Upton <oupton@google.com>,
	Huacai Chen <chenhuacai@kernel.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
	David Rientjes <rientjes@google.com>,
	KVM PPC <kvm-ppc@vger.kernel.org>,
	Jim Mattson <jmattson@google.com>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Sean Christopherson <seanjc@google.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Peter Shier <pshier@google.com>,
	Linux MIPS <linux-mips@vger.kernel.org>,
	Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [RFC PATCH 3/4] KVM: stats: Add ioctl commands to pull statistics in binary format
Date: Wed, 10 Mar 2021 17:05:01 +0000	[thread overview]
Message-ID: <8735x3x7lu.wl-maz@kernel.org> (raw)
In-Reply-To: <a475d935-e404-93dd-4c6d-a5f8038d8f4d@redhat.com>

On Wed, 10 Mar 2021 16:03:42 +0000,
Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> On 10/03/21 16:51, Marc Zyngier wrote:
> >> +	kvm_for_each_vcpu(j, vcpu, kvm) {
> >> +		pdata = data + VM_STAT_COUNT;
> >> +		for (i = 0; i < VCPU_STAT_COUNT; i++, pdata++)
> >> +			*pdata += *((u64 *)&vcpu->stat + i);
> > Do you really need the in-kernel copy? Why not directly organise the
> > data structures in a way that would allow a bulk copy using
> > copy_to_user()?
> 
> The result is built by summing per-vCPU counters, so that the counter
> updates are fast and do not require a lock.  So consistency basically
> cannot be guaranteed.

Sure, but I wonder whether there is scope for VM-global counters to be
maintained in parallel with per-vCPU counters if speed/efficiency is
of the essence (and this seems to be how it is sold in the cover
letter).

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
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kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

  reply	other threads:[~2021-03-10 17:06 UTC|newest]

Thread overview: 64+ 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 ` 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  0:30   ` Jing Zhang
2021-03-10  0:30   ` Jing Zhang
2021-03-10 14:19   ` Marc Zyngier
2021-03-10 14:19     ` Marc Zyngier
2021-03-10 14:19     ` Marc Zyngier
2021-03-10 18:51     ` Jing Zhang
2021-03-10 18:51       ` Jing Zhang
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  0:30   ` Jing Zhang
2021-03-10  0:30   ` Jing Zhang
2021-03-10 14:58   ` Marc Zyngier
2021-03-10 14:58     ` Marc Zyngier
2021-03-10 14:58     ` Marc Zyngier
2021-03-10 19:36     ` Jing Zhang
2021-03-10 19:36       ` Jing Zhang
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  0:30   ` Jing Zhang
2021-03-10 14:55   ` Paolo Bonzini
2021-03-10 14:55     ` Paolo Bonzini
2021-03-10 14:55     ` Paolo Bonzini
2021-03-10 21:41     ` Jing Zhang
2021-03-10 21:41       ` Jing Zhang
2021-03-10 21:41       ` Jing Zhang
2021-03-12 18:11       ` Paolo Bonzini
2021-03-12 18:11         ` Paolo Bonzini
2021-03-12 18:11         ` Paolo Bonzini
2021-03-12 22:27         ` Jing Zhang
2021-03-12 22:27           ` Jing Zhang
2021-03-12 22:27           ` Jing Zhang
2021-03-13  9:35           ` Paolo Bonzini
2021-03-13  9:35             ` Paolo Bonzini
2021-03-13  9:35             ` Paolo Bonzini
2021-03-15 22:31     ` Jing Zhang
2021-03-15 22:31       ` Jing Zhang
2021-03-15 22:31       ` Jing Zhang
2021-03-16 17:54       ` Paolo Bonzini
2021-03-16 17:54         ` Paolo Bonzini
2021-03-16 17:54         ` Paolo Bonzini
2021-03-10 15:51   ` Marc Zyngier
2021-03-10 15:51     ` Marc Zyngier
2021-03-10 16:03     ` Paolo Bonzini
2021-03-10 16:03       ` Paolo Bonzini
2021-03-10 16:03       ` Paolo Bonzini
2021-03-10 17:05       ` Marc Zyngier [this message]
2021-03-10 17:05         ` Marc Zyngier
2021-03-10 17:11         ` Paolo Bonzini
2021-03-10 17:11           ` Paolo Bonzini
2021-03-10 17:11           ` Paolo Bonzini
2021-03-10 17:31           ` Marc Zyngier
2021-03-10 17:31             ` Marc Zyngier
2021-03-10 17:44             ` Paolo Bonzini
2021-03-10 17:44               ` Paolo Bonzini
2021-03-10 17:44               ` Paolo Bonzini
2021-03-10 21:43               ` Jing Zhang
2021-03-10 21:43                 ` Jing Zhang
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
2021-03-10  0:30   ` Jing Zhang
2021-03-10  0:30   ` Jing Zhang

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