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 01/13] KVM: x86: Cache total page count to avoid traversing the memslot array
Date: Tue, 19 Oct 2021 22:24:11 +0000 [thread overview]
Message-ID: <YW9Fi128rYxiF1v3@google.com> (raw)
In-Reply-To: <d07f07cdd545ab1a495a9a0da06e43ad97c069a2.1632171479.git.maciej.szmigiero@oracle.com>
On Mon, Sep 20, 2021, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>
> There is no point in recalculating from scratch the total number of pages
> in all memslots each time a memslot is created or deleted.
>
> Just cache the value and update it accordingly on each such operation so
> the code doesn't need to traverse the whole memslot array each time.
>
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> ---
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 28ef14155726..65fdf27b9423 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11609,9 +11609,23 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
> const struct kvm_memory_slot *new,
> enum kvm_mr_change change)
> {
> - if (!kvm->arch.n_requested_mmu_pages)
> - kvm_mmu_change_mmu_pages(kvm,
> - kvm_mmu_calculate_default_mmu_pages(kvm));
> + if (change == KVM_MR_CREATE)
> + kvm->arch.n_memslots_pages += new->npages;
> + else if (change == KVM_MR_DELETE) {
> + WARN_ON(kvm->arch.n_memslots_pages < old->npages);
> + kvm->arch.n_memslots_pages -= old->npages;
> + }
> +
> + if (!kvm->arch.n_requested_mmu_pages) {
Hmm, once n_requested_mmu_pages is set it can't be unset. That means this can be
further optimized to skip avoid taking mmu_lock on flags-only changes (and
memslot movement). E.g.
if (!kvm->arch.n_requested_mmu_pages &&
(change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
}
It's a little risky, but kvm_vm_ioctl_set_nr_mmu_pages() would need to be modified
to allow clearing n_requested_mmu_pages and it already takes slots_lock, so IMO
it's ok to force kvm_vm_ioctl_set_nr_mmu_pages() to recalculate pages if it wants
to allow reverting back to the default.
> + u64 memslots_pages;
> + unsigned long nr_mmu_pages;
> +
> + memslots_pages = kvm->arch.n_memslots_pages * KVM_PERMILLE_MMU_PAGES;
> + do_div(memslots_pages, 1000);
> + nr_mmu_pages = max_t(typeof(nr_mmu_pages),
> + memslots_pages, KVM_MIN_ALLOC_MMU_PAGES);
"memslots_pages" is a bit of a misnomer. Any objection to avoiding naming problems
by explicitly casting to an "unsigned long" and simply operating on nr_mmu_pages?
nr_mmu_pages = (unsigned long)kvm->arch.n_memslots_pages;
nr_mmu_pages *= (KVM_PERMILLE_MMU_PAGES / 1000);
nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
E.g. the whole thing can be
if (!kvm->arch.n_requested_mmu_pages &&
(change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
unsigned long nr_mmu_pages;
if (change == KVM_MR_CREATE) {
kvm->arch.n_memslots_pages += new->npages;
} else {
WARN_ON(kvm->arch.n_memslots_pages < old->npages);
kvm->arch.n_memslots_pages -= old->npages;
}
nr_mmu_pages = (unsigned long)kvm->arch.n_memslots_pages;
nr_mmu_pages *= (KVM_PERMILLE_MMU_PAGES / 1000);
nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
}
> + kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
> + }
>
> kvm_mmu_slot_apply_flags(kvm, old, new, change);
>
next prev parent reply other threads:[~2021-10-19 22:24 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-20 21:38 [PATCH v5 00/13] KVM: Scalable memslots implementation Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 01/13] KVM: x86: Cache total page count to avoid traversing the memslot array Maciej S. Szmigiero
2021-10-19 22:24 ` Sean Christopherson [this message]
2021-10-19 22:31 ` Sean Christopherson
2021-10-20 18:40 ` Maciej S. Szmigiero
2021-10-20 18:41 ` Maciej S. Szmigiero
2021-10-20 19:01 ` Sean Christopherson
2021-11-01 22:29 ` Sean Christopherson
2021-11-03 11:59 ` Maciej S. Szmigiero
2021-11-03 14:47 ` Sean Christopherson
2021-11-03 15:38 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 02/13] KVM: x86: Don't call kvm_mmu_change_mmu_pages() if the count hasn't changed Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 03/13] KVM: Add "old" memslot parameter to kvm_arch_prepare_memory_region() Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 04/13] KVM: x86: Move n_memslots_pages recalc " Maciej S. Szmigiero
2021-10-19 22:38 ` Sean Christopherson
2021-10-20 18:41 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 05/13] KVM: Integrate gfn_to_memslot_approx() into search_memslots() Maciej S. Szmigiero
2021-10-19 23:38 ` Sean Christopherson
2021-10-20 18:41 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 06/13] KVM: Move WARN on invalid memslot index to update_memslots() Maciej S. Szmigiero
2021-10-19 23:42 ` Sean Christopherson
2021-09-20 21:38 ` [PATCH v5 07/13] KVM: Just resync arch fields when slots_arch_lock gets reacquired Maciej S. Szmigiero
2021-10-19 23:55 ` Sean Christopherson
2021-10-20 18:41 ` Maciej S. Szmigiero
2021-10-20 18:57 ` Sean Christopherson
2021-10-20 18:58 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 08/13] KVM: Resolve memslot ID via a hash table instead of via a static array Maciej S. Szmigiero
2021-10-20 0:43 ` Sean Christopherson
2021-10-20 18:42 ` Maciej S. Szmigiero
2021-10-20 22:39 ` Sean Christopherson
2021-10-21 14:15 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 09/13] KVM: Use interval tree to do fast hva lookup in memslots Maciej S. Szmigiero
2021-10-26 18:19 ` Sean Christopherson
2021-10-26 18:46 ` Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 10/13] KVM: s390: Introduce kvm_s390_get_gfn_end() Maciej S. Szmigiero
2021-09-20 21:38 ` [PATCH v5 11/13] KVM: Keep memslots in tree-based structures instead of array-based ones Maciej S. Szmigiero
2021-10-27 0:36 ` Sean Christopherson
2021-10-27 23:54 ` Sean Christopherson
2021-10-28 22:22 ` Sean Christopherson
2021-09-20 21:39 ` [PATCH v5 12/13] KVM: Optimize gfn lookup in kvm_zap_gfn_range() Maciej S. Szmigiero
2021-10-20 23:47 ` Sean Christopherson
2021-10-21 14:16 ` Maciej S. Szmigiero
2021-10-21 16:30 ` Sean Christopherson
2021-10-21 21:44 ` Maciej S. Szmigiero
2021-09-20 21:39 ` [PATCH v5 13/13] KVM: Optimize overlapping memslots check Maciej S. Szmigiero
2021-10-26 18:59 ` Sean Christopherson
2021-10-27 13:48 ` Maciej S. Szmigiero
2021-10-28 17:53 ` Sean Christopherson
2021-10-29 16:23 ` Maciej S. Szmigiero
2021-10-30 0:32 ` Sean Christopherson
2021-10-19 22:07 ` [PATCH v5 00/13] KVM: Scalable memslots implementation Sean Christopherson
2021-10-20 18:40 ` Maciej S. Szmigiero
2021-10-20 19:58 ` Sean Christopherson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YW9Fi128rYxiF1v3@google.com \
--to=seanjc@google.com \
--cc=aleksandar.qemu.devel@gmail.com \
--cc=borntraeger@de.ibm.com \
--cc=chenhuacai@kernel.org \
--cc=cohuck@redhat.com \
--cc=david@redhat.com \
--cc=frankja@linux.ibm.com \
--cc=imammedo@redhat.com \
--cc=imbrenda@linux.ibm.com \
--cc=james.morse@arm.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=julien.thierry.kdev@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mail@maciej.szmigiero.name \
--cc=maz@kernel.org \
--cc=paulus@ozlabs.org \
--cc=pbonzini@redhat.com \
--cc=suzuki.poulose@arm.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).