Re: [PATCH v5 09/13] KVM: Use interval tree to do fast hva lookup in memslots

From: Sean Christopherson <seanjc@google.com>
To: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Igor Mammedov <imammedo@redhat.com>,
	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>,
	Huacai Chen <chenhuacai@kernel.org>,
	Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
	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>,
	Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 09/13] KVM: Use interval tree to do fast hva lookup in memslots
Date: Tue, 26 Oct 2021 18:19:15 +0000	[thread overview]
Message-ID: <YXhGo/FpqUAuz7Td@google.com> (raw)
In-Reply-To: <89deea791ff7a5f4faa535edb9956e9863a564b8.1632171479.git.maciej.szmigiero@oracle.com>

On Mon, Sep 20, 2021, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> The current memslots implementation only allows quick binary search by gfn,
> quick lookup by hva is not possible - the implementation has to do a linear
> scan of the whole memslots array, even though the operation being performed
> might apply just to a single memslot.
> 
> This significantly hurts performance of per-hva operations with higher
> memslot counts.
> 
> Since hva ranges can overlap between memslots an interval tree is needed
> for tracking them.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> ---
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 50597608d085..7ed780996910 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -472,6 +472,12 @@ static void kvm_null_fn(void)
>  }
>  #define IS_KVM_NULL_FN(fn) ((fn) == (void *)kvm_null_fn)
>  
> +/* Iterate over each memslot intersecting [start, last] (inclusive) range */
> +#define kvm_for_each_memslot_in_hva_range(node, slots, start, last)	     \
> +	for (node = interval_tree_iter_first(&slots->hva_tree, start, last); \
> +	     node;							     \
> +	     node = interval_tree_iter_next(node, start, last))	     \

Similar to kvm_for_each_memslot_in_gfn_range(), this should use an opaque iterator
to hide the implementation details from the caller, e.g. to avoid having to define
a "struct interval_tree_node" and do container_of.