From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [virtio-dev] Re: [PATCH v11 6/6] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ Date: Wed, 21 Jun 2017 15:28:56 +0300 Message-ID: <20170621151922-mutt-send-email-mst@kernel.org> References: <1497004901-30593-1-git-send-email-wei.w.wang@intel.com> <1497004901-30593-7-git-send-email-wei.w.wang@intel.com> <20170620190343-mutt-send-email-mst@kernel.org> <5949E7C0.3050106@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <5949E7C0.3050106@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Wei Wang Cc: aarcange@redhat.com, virtio-dev@lists.oasis-open.org, riel@redhat.com, kvm@vger.kernel.org, qemu-devel@nongnu.org, amit.shah@redhat.com, liliang.opensource@gmail.com, dave.hansen@intel.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, cornelia.huck@de.ibm.com, pbonzini@redhat.com, akpm@linux-foundation.org, nilal@redhat.com, mgorman@techsingularity.net List-Id: virtualization@lists.linuxfoundation.org On Wed, Jun 21, 2017 at 11:28:00AM +0800, Wei Wang wrote: > On 06/21/2017 12:18 AM, Michael S. Tsirkin wrote: > > On Fri, Jun 09, 2017 at 06:41:41PM +0800, Wei Wang wrote: > > > - if (!virtqueue_indirect_desc_table_add(vq, desc, num)) { > > > + if (!virtqueue_indirect_desc_table_add(vq, desc, *num)) { > > > virtqueue_kick(vq); > > > - wait_event(vb->acked, virtqueue_get_buf(vq, &len)); > > > - vb->balloon_page_chunk.chunk_num = 0; > > > + if (busy_wait) > > > + while (!virtqueue_get_buf(vq, &len) && > > > + !virtqueue_is_broken(vq)) > > > + cpu_relax(); > > > + else > > > + wait_event(vb->acked, virtqueue_get_buf(vq, &len)); > > > > This is something I didn't previously notice. > > As you always keep a single buffer in flight, you do not > > really need indirect at all. Just add all descriptors > > in the ring directly, then kick. > > > > E.g. > > virtqueue_add_first > > virtqueue_add_next > > virtqueue_add_last > > > > ? > > > > You also want a flag to avoid allocations but there's no need to do it > > per descriptor, set it on vq. > > > > Without using the indirect table, I'm thinking about changing to use > the standard sg (i.e. struct scatterlist), instead of vring_desc, so that > we don't need to modify or add any new functions of virtqueue_add(). > > In this case, we will kmalloc an array of sgs in probe(), and we can add > the sgs one by one to the vq, which won't trigger the allocation of an > indirect table inside virtqueue_add(), and then kick when all are added. > > Best, > Wei And allocate headers too? This can work. API extensions aren't necessarily a bad idea though. The API I suggest above is preferable for the simple reason that it can work without INDIRECT flag support in hypervisor. I wonder which APIs would Nitesh find useful. -- MST