From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751690AbdG1IWp (ORCPT ); Fri, 28 Jul 2017 04:22:45 -0400 Received: from mga01.intel.com ([192.55.52.88]:13860 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751007AbdG1IWo (ORCPT ); Fri, 28 Jul 2017 04:22:44 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.40,424,1496127600"; d="scan'208";a="132297680" Message-ID: <597AF4EF.4020705@intel.com> Date: Fri, 28 Jul 2017 16:25:19 +0800 From: Wei Wang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mst@redhat.com, david@redhat.com, cornelia.huck@de.ibm.com, akpm@linux-foundation.org, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, mhocko@kernel.org, willy@infradead.org CC: virtio-dev@lists.oasis-open.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com Subject: Re: [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F_SG References: <1499863221-16206-1-git-send-email-wei.w.wang@intel.com> <1499863221-16206-6-git-send-email-wei.w.wang@intel.com> In-Reply-To: <1499863221-16206-6-git-send-email-wei.w.wang@intel.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/12/2017 08:40 PM, Wei Wang wrote: > Add a new feature, VIRTIO_BALLOON_F_SG, which enables to > transfer a chunk of ballooned (i.e. inflated/deflated) pages using > scatter-gather lists to the host. > > The implementation of the previous virtio-balloon is not very > efficient, because the balloon pages are transferred to the > host one by one. Here is the breakdown of the time in percentage > spent on each step of the balloon inflating process (inflating > 7GB of an 8GB idle guest). > > 1) allocating pages (6.5%) > 2) sending PFNs to host (68.3%) > 3) address translation (6.1%) > 4) madvise (19%) > > It takes about 4126ms for the inflating process to complete. > The above profiling shows that the bottlenecks are stage 2) > and stage 4). > > This patch optimizes step 2) by transferring pages to the host in > sgs. An sg describes a chunk of guest physically continuous pages. > With this mechanism, step 4) can also be optimized by doing address > translation and madvise() in chunks rather than page by page. > > With this new feature, the above ballooning process takes ~491ms > resulting in an improvement of ~88%. > I found a recent mm patch, bb01b64cfab7c22f3848cb73dc0c2b46b8d38499 , zeros all the ballooned pages, which is very time consuming. Tests show that the time to balloon 7G pages is increased from ~491 ms to 2.8 seconds with the above patch. How about moving the zero operation to the hypervisor? In this way, we will have a much faster balloon process. Best, Wei