From: Sean Christopherson <seanjc@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: shuah@kernel.org, kvm@vger.kernel.org, catalin.marinas@arm.com,
andrew.jones@linux.dev, dmatlack@google.com,
shan.gavin@gmail.com, bgardon@google.com, kvmarm@lists.linux.dev,
pbonzini@redhat.com, zhenyzha@redhat.com, will@kernel.org,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v6 3/8] KVM: Add support for using dirty ring in conjunction with bitmap
Date: Tue, 25 Oct 2022 00:08:31 +0000 [thread overview]
Message-ID: <Y1co/8GnSU7C+M0n@google.com> (raw)
In-Reply-To: <Y1ckxYst3tc0LCqb@google.com>
On Mon, Oct 24, 2022, Sean Christopherson wrote:
> On Sat, Oct 22, 2022, Marc Zyngier wrote:
> > On Fri, 21 Oct 2022 17:05:26 +0100, Sean Christopherson <seanjc@google.com> wrote:
> > >
> > > On Fri, Oct 21, 2022, Marc Zyngier wrote:
> > > > Because dirtying memory outside of a vcpu context makes it
> > > > incredibly awkward to handle a "ring full" condition?
> > >
> > > Kicking all vCPUs with the soft-full request isn't _that_ awkward.
> > > It's certainly sub-optimal, but if inserting into the per-VM ring is
> > > relatively rare, then in practice it's unlikely to impact guest
> > > performance.
> >
> > But there is *nothing* to kick here. The kernel is dirtying pages,
> > devices are dirtying pages (DMA), and there is no context associated
> > with that. Which is why a finite ring is the wrong abstraction.
>
> I don't follow. If there's a VM, KVM can always kick all vCPUs. Again, might
> be far from optimal, but it's an option. If there's literally no VM, then KVM
> isn't involved at all and there's no "ring vs. bitmap" decision.
Finally caught up in the other part of the thread that calls out that the devices
can't be stalled.
https://lore.kernel.org/all/87czakgmc0.wl-maz@kernel.org
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WARNING: multiple messages have this Message-ID (diff)
From: Sean Christopherson <seanjc@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Gavin Shan <gshan@redhat.com>,
kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,
kvm@vger.kernel.org, peterx@redhat.com, will@kernel.org,
catalin.marinas@arm.com, bgardon@google.com, shuah@kernel.org,
andrew.jones@linux.dev, dmatlack@google.com, pbonzini@redhat.com,
zhenyzha@redhat.com, james.morse@arm.com, suzuki.poulose@arm.com,
alexandru.elisei@arm.com, oliver.upton@linux.dev,
shan.gavin@gmail.com
Subject: Re: [PATCH v6 3/8] KVM: Add support for using dirty ring in conjunction with bitmap
Date: Tue, 25 Oct 2022 00:08:31 +0000 [thread overview]
Message-ID: <Y1co/8GnSU7C+M0n@google.com> (raw)
Message-ID: <20221025000831.6GZKDCr3uTekDGGP9DLLOniLcelPaYx6top-C1u7Z30@z> (raw)
In-Reply-To: <Y1ckxYst3tc0LCqb@google.com>
On Mon, Oct 24, 2022, Sean Christopherson wrote:
> On Sat, Oct 22, 2022, Marc Zyngier wrote:
> > On Fri, 21 Oct 2022 17:05:26 +0100, Sean Christopherson <seanjc@google.com> wrote:
> > >
> > > On Fri, Oct 21, 2022, Marc Zyngier wrote:
> > > > Because dirtying memory outside of a vcpu context makes it
> > > > incredibly awkward to handle a "ring full" condition?
> > >
> > > Kicking all vCPUs with the soft-full request isn't _that_ awkward.
> > > It's certainly sub-optimal, but if inserting into the per-VM ring is
> > > relatively rare, then in practice it's unlikely to impact guest
> > > performance.
> >
> > But there is *nothing* to kick here. The kernel is dirtying pages,
> > devices are dirtying pages (DMA), and there is no context associated
> > with that. Which is why a finite ring is the wrong abstraction.
>
> I don't follow. If there's a VM, KVM can always kick all vCPUs. Again, might
> be far from optimal, but it's an option. If there's literally no VM, then KVM
> isn't involved at all and there's no "ring vs. bitmap" decision.
Finally caught up in the other part of the thread that calls out that the devices
can't be stalled.
https://lore.kernel.org/all/87czakgmc0.wl-maz@kernel.org
next prev parent reply other threads:[~2022-10-25 0:08 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-11 6:14 [PATCH v6 0/8] KVM: arm64: Enable ring-based dirty memory tracking Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 1/8] KVM: x86: Introduce KVM_REQ_RING_SOFT_FULL Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-20 22:42 ` Sean Christopherson
2022-10-20 22:42 ` Sean Christopherson
2022-10-21 5:54 ` Gavin Shan
2022-10-21 5:54 ` Gavin Shan
2022-10-21 15:25 ` Sean Christopherson
2022-10-21 15:25 ` Sean Christopherson
2022-10-21 23:03 ` Gavin Shan
2022-10-21 23:03 ` Gavin Shan
2022-10-21 23:48 ` Sean Christopherson
2022-10-21 23:48 ` Sean Christopherson
2022-10-22 0:16 ` Gavin Shan
2022-10-22 0:16 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 2/8] KVM: x86: Move declaration of kvm_cpu_dirty_log_size() to kvm_dirty_ring.h Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 3/8] KVM: Add support for using dirty ring in conjunction with bitmap Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-18 16:07 ` Peter Xu
2022-10-18 16:07 ` Peter Xu
2022-10-18 22:20 ` Gavin Shan
2022-10-18 22:20 ` Gavin Shan
2022-10-20 18:58 ` Oliver Upton
2022-10-20 18:58 ` Oliver Upton
2022-10-20 23:44 ` Sean Christopherson
2022-10-20 23:44 ` Sean Christopherson
2022-10-21 8:06 ` Marc Zyngier
2022-10-21 8:06 ` Marc Zyngier
2022-10-21 16:05 ` Sean Christopherson
2022-10-21 16:05 ` Sean Christopherson
2022-10-22 8:27 ` Gavin Shan
2022-10-22 8:27 ` Gavin Shan
2022-10-22 10:54 ` Marc Zyngier
2022-10-22 10:54 ` Marc Zyngier
2022-10-22 10:33 ` Marc Zyngier
2022-10-22 10:33 ` Marc Zyngier
2022-10-24 23:50 ` Sean Christopherson
2022-10-24 23:50 ` Sean Christopherson
2022-10-25 0:08 ` Sean Christopherson [this message]
2022-10-25 0:08 ` Sean Christopherson
2022-10-25 0:24 ` Oliver Upton
2022-10-25 0:24 ` Oliver Upton
2022-10-25 7:31 ` Marc Zyngier
2022-10-25 7:31 ` Marc Zyngier
2022-10-25 17:47 ` Sean Christopherson
2022-10-25 17:47 ` Sean Christopherson
2022-10-27 8:29 ` Marc Zyngier
2022-10-27 8:29 ` Marc Zyngier
2022-10-27 17:44 ` Sean Christopherson
2022-10-27 17:44 ` Sean Christopherson
2022-10-27 18:30 ` Marc Zyngier
2022-10-27 18:30 ` Marc Zyngier
2022-10-27 19:09 ` Sean Christopherson
2022-10-27 19:09 ` Sean Christopherson
2022-10-28 6:43 ` Gavin Shan
2022-10-28 6:43 ` Gavin Shan
2022-10-28 16:51 ` Sean Christopherson
2022-10-28 16:51 ` Sean Christopherson
2022-10-31 3:37 ` Gavin Shan
2022-10-31 3:37 ` Gavin Shan
2022-10-31 9:08 ` Marc Zyngier
2022-10-31 9:08 ` Marc Zyngier
2022-10-31 22:48 ` Gavin Shan
2022-10-31 22:48 ` Gavin Shan
2022-10-25 7:22 ` Marc Zyngier
2022-10-25 7:22 ` Marc Zyngier
2022-10-21 10:13 ` Gavin Shan
2022-10-21 10:13 ` Gavin Shan
2022-10-21 23:20 ` Sean Christopherson
2022-10-21 23:20 ` Sean Christopherson
2022-10-22 0:33 ` Gavin Shan
2022-10-22 0:33 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 4/8] KVM: arm64: Enable ring-based dirty memory tracking Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 5/8] KVM: selftests: Enable KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP if possible Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 6/8] KVM: selftests: Use host page size to map ring buffer in dirty_log_test Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 7/8] KVM: selftests: Clear dirty ring states between two modes " Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 8/8] KVM: selftests: Automate choosing dirty ring size " Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:23 ` [PATCH v6 0/8] KVM: arm64: Enable ring-based dirty memory tracking Gavin Shan
2022-10-11 6:23 ` Gavin Shan
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