From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id 0CC76A2EDB for ; Fri, 6 Sep 2019 18:02:05 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id 5D6831F41F; Fri, 6 Sep 2019 18:02:04 +0200 (CEST) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id 08EB31F40E for ; Fri, 6 Sep 2019 18:02:03 +0200 (CEST) Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2A27F305883E; Fri, 6 Sep 2019 16:02:02 +0000 (UTC) Received: from [10.36.112.25] (ovpn-112-25.ams2.redhat.com [10.36.112.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DF6C75EE1D; Fri, 6 Sep 2019 16:01:55 +0000 (UTC) To: Joyce Kong , dev@dpdk.org Cc: nd@arm.com, tiwei.bie@intel.com, zhihong.wang@intel.com, amorenoz@redhat.com, xiao.w.wang@intel.com, yong.liu@intel.com, jfreimann@redhat.com, honnappa.nagarahalli@arm.com, gavin.hu@arm.com References: <1567769688-34413-1-git-send-email-joyce.kong@arm.com> <1567769688-34413-2-git-send-email-joyce.kong@arm.com> From: Maxime Coquelin Openpgp: preference=signencrypt Autocrypt: addr=maxime.coquelin@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <1567769688-34413-2-git-send-email-joyce.kong@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Fri, 06 Sep 2019 16:02:02 +0000 (UTC) Subject: Re: [dpdk-dev] [PATCH v2 1/2] virtio: one way barrier for packed vring desc avail flags X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Hi Joyce, On 9/6/19 1:34 PM, Joyce Kong wrote: > In case VIRTIO_F_ORDER_PLATFORM(36) is not negotiated, then the frontend > and backend are assumed to be implemented in software, that is they can > run on identical CPUs in an SMP configuration. Thus a weak form of memory > barriers like rte_smp_r/wmb, other than rte_cio_r/wmb, is sufficient for > this case(vq->hw->weak_barriers == 1) and yields better performance. > For the above case, this patch helps yielding even better performance > by replacing the two-way barriers with C11 one-way barriers. > > Meanwhile, a read barrier is required to ensure ordering between > descriptor's flags and content reads[1]. With C11, load-acquire can > enforce the ordering instead of rmb barrier. > > [1]https://patchwork.dpdk.org/patch/49109/ > > Signed-off-by: Joyce Kong > Reviewed-by: Gavin Hu > Reviewed-by: Phil Yang > --- > drivers/net/virtio/virtio_rxtx.c | 26 ++++++++++++++++++------ > drivers/net/virtio/virtio_user/virtio_user_dev.c | 6 +++++- > lib/librte_vhost/vhost.h | 2 +- > lib/librte_vhost/virtio_net.c | 11 +++++----- > 4 files changed, 31 insertions(+), 14 deletions(-) > > diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c > index 27ead19..2a2153c 100644 > --- a/drivers/net/virtio/virtio_rxtx.c > +++ b/drivers/net/virtio/virtio_rxtx.c > @@ -456,8 +456,14 @@ virtqueue_enqueue_recv_refill_packed(struct virtqueue *vq, > vq->vq_desc_head_idx = dxp->next; > if (vq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END) > vq->vq_desc_tail_idx = vq->vq_desc_head_idx; > - virtio_wmb(hw->weak_barriers); > - start_dp[idx].flags = flags; > + > + if (hw->weak_barriers) > + __atomic_store_n(&start_dp[idx].flags, flags, > + __ATOMIC_RELEASE); > + else { > + rte_cio_wmb(); > + start_dp[idx].flags = flags; > + } It looks good to me. I just wonder whether it would be cleaner to put that in an inline function: static inline void virtqueue_store_flags_packed() Same for the fetch.