From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zang Hongyong Subject: Re: [PATCH 0/2] vhot-net: Use kvm_memslots instead of vhost_memory to translate GPA to HVA Date: Fri, 16 Dec 2011 16:18:45 +0800 Message-ID: <4EEAFEE5.3000406@huawei.com> References: <1324013528-3663-1-git-send-email-zanghongyong@huawei.com> <1324019151.4496.9.camel@lappy> <4EEAF5D1.2080805@huawei.com> <1324022358.4496.25.camel@lappy> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7BIT Cc: linux-kernel@vger.kernel.org, mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, xiaowei.yang@huawei.com, hanweidong@huawei.com, wusongwei@huawei.com To: Sasha Levin Return-path: In-reply-to: <1324022358.4496.25.camel@lappy> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 于 2011/12/16,星期五 15:59, Sasha Levin 写道: > On Fri, 2011-12-16 at 15:40 +0800, Zang Hongyong wrote: >> 于 2011/12/16,星期五 15:05, Sasha Levin 写道: >>> On Fri, 2011-12-16 at 13:32 +0800, zanghongyong@huawei.com wrote: >>>> From: Hongyong Zang >>>> >>>> Vhost-net uses its own vhost_memory, which results from user space (qemu) info, >>>> to translate GPA to HVA. Since kernel's kvm structure already maintains the >>>> address relationship in its member *kvm_memslots*, these patches use kernel's >>>> kvm_memslots directly without the need of initialization and maintenance of >>>> vhost_memory. >>> Conceptually, vhost isn't aware of KVM - it's just a driver which moves >>> data from vq to a tap device and back. You can't simply add KVM specific >>> code into vhost. >>> >>> Whats the performance benefit? >>> >> But vhost-net is only used in virtualization situation. vhost_memory is >> maintained >> by user space qemu. >> In this way, the memory relationship can be accquired from kernel >> without the >> need of maintainence of vhost_memory from qemu. > You can't assume that vhost-* is used only along with qemu/kvm. Just as > virtio has more uses than just virtualization (heres one: > https://lkml.org/lkml/2011/10/25/139 ), there are more uses for vhost as > well. > > There has been a great deal of effort to keep vhost and kvm untangled. > One example is the memory translation it has to do, another one is the > eventfd/irqfd thing it does just so it could signal an IRQ in the guest > instead of accessing the guest directly. > > If you do see a great performance increase when tying vhost and KVM > together, it may be worth it to create some sort of an in-kernel > vhost-kvm bridging thing, but if the performance isn't noticeable we're > better off just leaving it as is and keeping the vhost code general. > Thanks for your explanation. Since memory layout is seldom changed after guest boots, the situation manily occurs during initialization. There's no need for vhost-kvm bridge now.