From: Sean Christopherson <seanjc@google.com>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: Ricardo Koller <ricarkol@google.com>,
Marc Zyngier <maz@kernel.org>,
pbonzini@redhat.com, yuzenghui@huawei.com, dmatlack@google.com,
kvm@vger.kernel.org, kvmarm@lists.linux.dev, qperret@google.com,
catalin.marinas@arm.com, andrew.jones@linux.dev,
alexandru.elisei@arm.com, suzuki.poulose@arm.com,
eric.auger@redhat.com, gshan@redhat.com, reijiw@google.com,
rananta@google.com, bgardon@google.com, ricarkol@gmail.com
Subject: Re: [PATCH 6/9] KVM: arm64: Split huge pages when dirty logging is enabled
Date: Tue, 31 Jan 2023 01:18:15 +0000 [thread overview]
Message-ID: <Y9hsV02TpQeoB0oN@google.com> (raw)
In-Reply-To: <Y9g0KGmsZqAZiTSP@google.com>
On Mon, Jan 30, 2023, Oliver Upton wrote:
> I think that Marc's suggestion of having userspace configure this is
> sound. After all, userspace _should_ know the granularity of the backing
> source it chose for guest memory.
>
> We could also interpret a cache size of 0 to signal that userspace wants
> to disable eager page split for a VM altogether. It is entirely possible that
> the user will want a differing QoS between slice-of-hardware and
> overcommitted VMs.
Maybe. It's also entirely possible that QoS is never factored in, e.g. if QoS
guarantees for all VMs on a system are better met by enabling eager splitting
across the board.
There are other reasons to use module/kernel params beyond what Marc listed, e.g.
to let the user opt out even when something is on by default. x86's TDP MMU has
benefited greatly from downstream users being able to do A/B performance testing
this way. I suspect x86's eager_page_split knob was added largely for this
reason, e.g. to easily see how a specific workload is affected by eager splitting.
That seems like a reasonable fit on the ARM side as well.
IMO, we should try to avoid new uAPI without a proven need, especially if we're
considering throwing something into memslots. AFAIK, module params, at least on
the x86 side of things, aren't considered immutable ABI (or maybe it's just that
we haven't modified/removed one recently that folks care about).
next prev parent reply other threads:[~2023-01-31 1:18 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-13 3:49 [PATCH 0/9] KVM: arm64: Eager Huge-page splitting for dirty-logging Ricardo Koller
2023-01-13 3:49 ` [PATCH 1/9] KVM: arm64: Add KVM_PGTABLE_WALK_REMOVED into ctx->flags Ricardo Koller
2023-01-24 0:51 ` Ben Gardon
2023-01-24 0:56 ` Oliver Upton
2023-01-24 16:32 ` Ricardo Koller
2023-01-24 18:00 ` Ben Gardon
2023-01-26 18:48 ` Ricardo Koller
2023-01-24 16:30 ` Ricardo Koller
2023-01-13 3:49 ` [PATCH 2/9] KVM: arm64: Add helper for creating removed stage2 subtrees Ricardo Koller
2023-01-14 17:58 ` kernel test robot
2023-01-24 0:55 ` Ben Gardon
2023-01-24 16:35 ` Ricardo Koller
2023-01-24 17:07 ` Oliver Upton
2023-01-13 3:49 ` [PATCH 3/9] KVM: arm64: Add kvm_pgtable_stage2_split() Ricardo Koller
2023-01-24 1:03 ` Ben Gardon
2023-01-24 16:46 ` Ricardo Koller
2023-01-24 17:11 ` Oliver Upton
2023-01-24 17:18 ` Ricardo Koller
2023-01-24 17:48 ` David Matlack
2023-01-24 20:28 ` Oliver Upton
2023-02-06 9:20 ` Zheng Chuan
2023-02-06 16:28 ` Ricardo Koller
2023-01-13 3:49 ` [PATCH 4/9] KVM: arm64: Refactor kvm_arch_commit_memory_region() Ricardo Koller
2023-01-13 3:49 ` [PATCH 5/9] KVM: arm64: Add kvm_uninit_stage2_mmu() Ricardo Koller
2023-01-13 3:49 ` [PATCH 6/9] KVM: arm64: Split huge pages when dirty logging is enabled Ricardo Koller
2023-01-24 17:52 ` Ben Gardon
2023-01-24 22:19 ` Oliver Upton
2023-01-24 22:45 ` Oliver Upton
2023-01-26 18:45 ` Ricardo Koller
2023-01-26 19:25 ` Ricardo Koller
2023-01-26 20:10 ` Marc Zyngier
2023-01-27 15:45 ` Ricardo Koller
2023-01-30 21:18 ` Oliver Upton
2023-01-31 1:18 ` Sean Christopherson [this message]
2023-01-31 17:45 ` Oliver Upton
2023-01-31 17:54 ` Sean Christopherson
2023-01-31 19:06 ` Oliver Upton
2023-01-31 18:01 ` David Matlack
2023-01-31 18:19 ` Ricardo Koller
2023-01-31 18:35 ` Oliver Upton
2023-01-31 10:31 ` Marc Zyngier
2023-01-31 10:28 ` Marc Zyngier
2023-02-06 16:35 ` Ricardo Koller
2023-01-13 3:49 ` [PATCH 7/9] KVM: arm64: Open-code kvm_mmu_write_protect_pt_masked() Ricardo Koller
2023-01-13 3:49 ` [PATCH 8/9] KVM: arm64: Split huge pages during KVM_CLEAR_DIRTY_LOG Ricardo Koller
2023-01-13 3:50 ` [PATCH 9/9] KVM: arm64: Use local TLBI on permission relaxation Ricardo Koller
2023-01-24 0:48 ` [PATCH 0/9] KVM: arm64: Eager Huge-page splitting for dirty-logging Ben Gardon
2023-01-24 16:50 ` Ricardo Koller
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