From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Wang Subject: Re: [virtio-dev] Re: [PATCH v11 6/6] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ Date: Wed, 12 Jul 2017 20:57:10 +0800 Message-ID: <59661CA6.5040903__26059.3146471821$1499864090$gmane$org@intel.com> 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> <20170621151922-mutt-send-email-mst@kernel.org> <594B8287.6000706@intel.com> <20170628175956-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170628175956-mutt-send-email-mst@kernel.org> 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: "Michael S. Tsirkin" 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" , "Hansen, Dave" , "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 06/28/2017 11:01 PM, Michael S. Tsirkin wrote: > On Thu, Jun 22, 2017 at 04:40:39PM +0800, Wei Wang wrote: >> On 06/21/2017 08:28 PM, Michael S. Tsirkin wrote: >>> 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. >> OK, probably we don't need to add a desc to the vq - we can just use >> the vq's desc, like this: >> >> int virtqueue_add_first(struct virtqueue *_vq, >> uint64_t addr, >> uint32_t len, >> bool in, >> unsigned int *idx) { >> >> ... >> uint16_t desc_flags = in ? VRING_DESC_F_NEXT | VRING_DESC_F_WRITE : >> VRING_DESC_F_NEXT; >> >> vq->vring.desc[vq->free_head].addr = addr; >> vq->vring.desc[vq->free_head].len = len; >> vq->vring.desc[vq->free_head].flags = cpu_to_virtio16(_vq->vdev, flags); >> /* return to the caller the desc id */ >> *idx = vq->free_head; >> ... >> } >> >> int virtqueue_add_next(struct virtqueue *_vq, >> uint64_t addr, >> uint32_t len, >> bool in, >> bool end, >> unsigned int *idx) { >> ... >> vq->vring.desc[*idx].next = vq->free_head; >> vq->vring.desc[vq->free_head].addr = addr; >> ... >> if (end) >> remove the VRING_DESC_F_NEXT flag >> } >> > Add I would say add-last. > >> What do you think? We can also combine the two functions into one. >> >> >> >> Best, >> Wei > With an enum? Yes that's also an option. > Thanks for the suggestion. I shifted it a little bit, please have a check the latest v12 patches that I just sent out. Best, Wei