From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Ben Gardon <bgardon@google.com>
Cc: Marc Zyngier <maz@kernel.org>, Paul Mackerras <paulus@ozlabs.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
David Hildenbrand <david@redhat.com>,
Cornelia Huck <cohuck@redhat.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org,
kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
linux-kernel@vger.kernel.org, Peter Feiner <pfeiner@google.com>,
Peter Shier <pshier@google.com>,
Junaid Shahid <junaids@google.com>,
Christoffer Dall <christoffer.dall@arm.com>
Subject: Re: [PATCH 10/21] KVM: x86/mmu: Make __GFP_ZERO a property of the memory cache
Date: Mon, 22 Jun 2020 12:40:55 -0700 [thread overview]
Message-ID: <20200622194055.GC6151@linux.intel.com> (raw)
In-Reply-To: <CANgfPd9_BR_2NThfEs8faDxWeooZ6OeF2HAB5mUmted5sHwDPg@mail.gmail.com>
On Wed, Jun 10, 2020 at 11:57:32AM -0700, Ben Gardon wrote:
> > ---
> > arch/x86/include/asm/kvm_host.h | 1 +
> > arch/x86/kvm/mmu/mmu.c | 7 ++++++-
> > 2 files changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index e7a427547557..fb99e6776e27 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -251,6 +251,7 @@ struct kvm_kernel_irq_routing_entry;
> > */
> > struct kvm_mmu_memory_cache {
> > int nobjs;
> > + gfp_t gfp_zero;
> This would make more sense to me if it could be used for general extra
> gfp flags and was called gfp_flags or something, or it was a boolean
> that was later translated into the flag being set. Storing the
> gfp_zero flag here is a little counter-intuitive. Probably not worth
> changing unless you're sending out a v2 for some other reason.
Ideally, this would be a generic gfp_flags field, but that's basically a
non-starter for patch 5, which uses GFP_ATOMIC for the "oh crap the cache
is empty" error handling. Allowing arbitrary flags would be a mess.
I went with storing a full gfp_t because that produces more optimal code.
This isn't a super critical path and it's only a few cycles, but it seems
worthwhile given the frequency with which this code will be called, and
since this happens under mmu_lock.
348 gfp_flags |= mc->gfp_zero;
0x00000000000058ab <+59>: mov 0x4(%rbx),%eax
0x00000000000058ae <+62>: or $0x400cc0,%eax
versus
349 gfp_flags |= __GFP_ZERO;
0x00000000000058a7 <+55>: cmpb $0x1,0x4(%rbx)
0x00000000000058ab <+59>: mov 0x8(%rbx),%rdi <-- unrelated interleaved code
0x00000000000058af <+63>: sbb %eax,%eax
0x00000000000058b1 <+65>: xor %al,%al
0x00000000000058b3 <+67>: add $0x400dc0,%eax
next prev parent reply other threads:[~2020-06-22 19:41 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-05 21:38 [PATCH 00/21] KVM: Cleanup and unify kvm_mmu_memory_cache usage Sean Christopherson
2020-06-05 21:38 ` [PATCH 01/21] KVM: x86/mmu: Track the associated kmem_cache in the MMU caches Sean Christopherson
2020-06-09 21:07 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 02/21] KVM: x86/mmu: Consolidate "page" variant of memory cache helpers Sean Christopherson
2020-06-09 22:54 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 03/21] KVM: x86/mmu: Use consistent "mc" name for kvm_mmu_memory_cache locals Sean Christopherson
2020-06-10 22:03 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 04/21] KVM: x86/mmu: Remove superfluous gotos from mmu_topup_memory_caches() Sean Christopherson
2020-06-09 22:57 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 05/21] KVM: x86/mmu: Try to avoid crashing KVM if a MMU memory cache is empty Sean Christopherson
2020-06-10 22:12 ` Ben Gardon
2020-06-17 0:53 ` Sean Christopherson
2020-06-17 16:36 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 06/21] KVM: x86/mmu: Move fast_page_fault() call above mmu_topup_memory_caches() Sean Christopherson
2020-06-09 23:03 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 07/21] KVM: x86/mmu: Topup memory caches after walking GVA->GPA Sean Christopherson
2020-06-10 22:34 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 08/21] KVM: x86/mmu: Clean up the gorilla math in mmu_topup_memory_caches() Sean Christopherson
2020-06-10 22:20 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 09/21] KVM: x86/mmu: Separate the memory caches for shadow pages and gfn arrays Sean Christopherson
2020-06-09 23:56 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 10/21] KVM: x86/mmu: Make __GFP_ZERO a property of the memory cache Sean Christopherson
2020-06-10 18:57 ` Ben Gardon
2020-06-22 19:40 ` Sean Christopherson [this message]
2020-06-05 21:38 ` [PATCH 11/21] KVM: x86/mmu: Zero allocate shadow pages (outside of mmu_lock) Sean Christopherson
2020-06-10 18:49 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 12/21] KVM: x86/mmu: Skip filling the gfn cache for guaranteed direct MMU topups Sean Christopherson
2020-06-10 18:52 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 13/21] KVM: x86/mmu: Prepend "kvm_" to memory cache helpers that will be global Sean Christopherson
2020-06-10 18:56 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 14/21] KVM: Move x86's version of struct kvm_mmu_memory_cache to common code Sean Christopherson
2020-06-10 19:01 ` Ben Gardon
2020-06-10 21:58 ` Ben Gardon
2020-06-22 16:57 ` Sean Christopherson
2020-06-11 7:42 ` Marc Zyngier
2020-06-05 21:38 ` [PATCH 15/21] KVM: Move x86's MMU memory cache helpers to common KVM code Sean Christopherson
2020-06-10 20:24 ` Ben Gardon
2020-06-05 21:38 ` [PATCH 16/21] KVM: arm64: Drop @max param from mmu_topup_memory_cache() Sean Christopherson
2020-06-10 22:00 ` Ben Gardon
2020-06-11 15:59 ` Sean Christopherson
2020-06-05 21:38 ` [PATCH 17/21] KVM: arm64: Use common code's approach for __GFP_ZERO with memory caches Sean Christopherson
2020-06-11 7:59 ` Marc Zyngier
2020-06-11 15:43 ` Sean Christopherson
2020-06-11 15:51 ` Marc Zyngier
2020-06-05 21:38 ` [PATCH 18/21] KVM: arm64: Use common KVM implementation of MMU " Sean Christopherson
2020-06-11 8:01 ` Marc Zyngier
2020-06-11 15:46 ` Sean Christopherson
2020-06-05 21:38 ` [PATCH 19/21] KVM: MIPS: Drop @max param from mmu_topup_memory_cache() Sean Christopherson
2020-06-08 8:56 ` Huacai Chen
2020-06-05 21:38 ` [PATCH 20/21] KVM: MIPS: Account pages used for GPA page tables Sean Christopherson
2020-06-08 8:56 ` Huacai Chen
2020-06-05 21:38 ` [PATCH 21/21] KVM: MIPS: Use common KVM implementation of MMU memory caches Sean Christopherson
2020-06-08 8:57 ` Huacai Chen
2020-06-11 8:06 ` [PATCH 00/21] KVM: Cleanup and unify kvm_mmu_memory_cache usage Marc Zyngier
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