From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id 838C21BCAD for ; Thu, 20 Dec 2018 15:03:28 +0100 (CET) Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C118A3E2CF; Thu, 20 Dec 2018 14:03:27 +0000 (UTC) Received: from redhat.com (ovpn-122-182.rdu2.redhat.com [10.10.122.182]) by smtp.corp.redhat.com (Postfix) with SMTP id EEC321019629; Thu, 20 Dec 2018 14:03:21 +0000 (UTC) Date: Thu, 20 Dec 2018 09:03:21 -0500 From: "Michael S. Tsirkin" To: Tiwei Bie Cc: Maxime Coquelin , dev@dpdk.org, i.maximets@samsung.com, zhihong.wang@intel.com, jfreiman@redhat.com Message-ID: <20181220090253-mutt-send-email-mst@kernel.org> References: <20181219092952.25728-1-maxime.coquelin@redhat.com> <20181220044446.GB21484@dpdk-tbie.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181220044446.GB21484@dpdk-tbie.sh.intel.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 20 Dec 2018 14:03:27 +0000 (UTC) Subject: Re: [dpdk-dev] [PATCH v2] vhost: batch used descs chains write-back with packed ring 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: , X-List-Received-Date: Thu, 20 Dec 2018 14:03:28 -0000 On Thu, Dec 20, 2018 at 12:44:46PM +0800, Tiwei Bie wrote: > On Wed, Dec 19, 2018 at 10:29:52AM +0100, Maxime Coquelin wrote: > > Instead of writing back descriptors chains in order, let's > > write the first chain flags last in order to improve batching. > > > > With Kernel's pktgen benchmark, ~3% performance gain is measured. > > > > Signed-off-by: Maxime Coquelin > > --- > > > > V2: > > Revert back to initial implementation to have a write > > barrier before every descs flags store, but still > > store first desc flags last. (Missing barrier reported > > by Ilya) > > > > > > lib/librte_vhost/virtio_net.c | 19 ++++++++++++++++--- > > 1 file changed, 16 insertions(+), 3 deletions(-) > > > > diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c > > index 8c657a101..de436af79 100644 > > --- a/lib/librte_vhost/virtio_net.c > > +++ b/lib/librte_vhost/virtio_net.c > > @@ -97,6 +97,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, > > { > > int i; > > uint16_t used_idx = vq->last_used_idx; > > + uint16_t head_idx = vq->last_used_idx; > > + uint16_t head_flags = 0; > > > > /* Split loop in two to save memory barriers */ > > for (i = 0; i < vq->shadow_used_idx; i++) { > > @@ -126,12 +128,17 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, > > flags &= ~VRING_DESC_F_AVAIL; > > } > > > > - vq->desc_packed[vq->last_used_idx].flags = flags; > > + if (i > 0) { > > + vq->desc_packed[vq->last_used_idx].flags = flags; > > > > - vhost_log_cache_used_vring(dev, vq, > > + vhost_log_cache_used_vring(dev, vq, > > vq->last_used_idx * > > sizeof(struct vring_packed_desc), > > sizeof(struct vring_packed_desc)); > > + } else { > > + head_idx = vq->last_used_idx; > > + head_flags = flags; > > + } > > > > vq->last_used_idx += vq->shadow_used_packed[i].count; > > if (vq->last_used_idx >= vq->size) { > > @@ -140,7 +147,13 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, > > } > > } > > > > - rte_smp_wmb(); > > + vq->desc_packed[head_idx].flags = head_flags; > > + > > + vhost_log_cache_used_vring(dev, vq, > > + vq->last_used_idx * > > Should be head_idx. > > > + sizeof(struct vring_packed_desc), > > + sizeof(struct vring_packed_desc)); > > + > > vq->shadow_used_idx = 0; > > A wmb() is needed before log_cache_sync? > > > vhost_log_cache_sync(dev, vq); Probably smarter to have the wmb in there. This way we can skip it if not logging. > > } > > -- > > 2.17.2 > >