From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Roman Kagan <rkagan@virtuozzo.com>
Cc: kvm@vger.kernel.org, x86@kernel.org,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"K. Y. Srinivasan" <kys@microsoft.com>,
"Haiyang Zhang" <haiyangz@microsoft.com>,
"Stephen Hemminger" <sthemmin@microsoft.com>,
"Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>,
"Mohammed Gamal" <mmorsy@redhat.com>,
"Cathy Avery" <cavery@redhat.com>,
"Wanpeng Li" <wanpeng.li@hotmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 3/5] KVM: x86: hyperv: use get_vcpu_by_vpidx() in kvm_hv_flush_tlb()
Date: Fri, 29 Jun 2018 17:21:47 +0200 [thread overview]
Message-ID: <87a7rdd3ec.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20180629150104.GE15656@rkaganb.sw.ru> (Roman Kagan's message of "Fri, 29 Jun 2018 18:01:05 +0300")
Roman Kagan <rkagan@virtuozzo.com> writes:
> On Fri, Jun 29, 2018 at 04:14:53PM +0200, Vitaly Kuznetsov wrote:
>> VP_INDEX almost always matches VCPU id and get_vcpu_by_vpidx() is fast,
>> use it instead of traversing full vCPU list every time.
>>
>> To support the change switch kvm_make_vcpus_request_mask() to checking
>> vcpu_id instead of vcpu index,
>
> I'm afraid you can't do this: vcpu_id (== apic id) can be sparse, i.e.
> it's not very well suited for bitmaps and can exceed the max number of
> vcpus.
True. The bitmap should be of KVM_MAX_VCPU_ID size, not
KVM_MAX_VCPUS.
Unfortunately there's no convenient way to get VCPU idx from VCPU
id, kvm_vcpu_get_idx() just walks the whole list :-( I see two possible
options:
1) Add vcpu_idx fields to struct kvm_vcpu
2) Keep the change expecting masks of KVM_MAX_VCPU_ID in
kvm_make_vcpus_request_mask(). KVM_MAX_VCPU_ID is currently 1023 so our
bitmaps will be 16 longs long. Not sure if it's too much.
--
Vitaly
next prev parent reply other threads:[~2018-06-29 15:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-29 14:14 [PATCH v3 0/5] KVM: x86: hyperv: PV IPI support for Windows guests Vitaly Kuznetsov
2018-06-29 14:14 ` [PATCH v3 1/5] KVM: x86: hyperv: enforce vp_index < KVM_MAX_VCPUS Vitaly Kuznetsov
2018-06-29 14:14 ` [PATCH v3 2/5] KVM: x86: hyperv: optimize 'all cpus' case in kvm_hv_flush_tlb() Vitaly Kuznetsov
2018-06-29 14:14 ` [PATCH v3 3/5] KVM: x86: hyperv: use get_vcpu_by_vpidx() " Vitaly Kuznetsov
2018-06-29 15:01 ` Roman Kagan
2018-06-29 15:21 ` Vitaly Kuznetsov [this message]
2018-06-29 16:26 ` Roman Kagan
2018-06-29 16:47 ` Vitaly Kuznetsov
2018-06-29 16:53 ` Roman Kagan
2018-06-29 14:14 ` [PATCH v3 4/5] x86/hyper-v: rename ipi_arg_{ex,non_ex} structures Vitaly Kuznetsov
2018-06-29 14:14 ` [PATCH v3 5/5] KVM: x86: hyperv: implement PV IPI send hypercalls Vitaly Kuznetsov
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