From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by dpdk.org (Postfix) with ESMTP id 2F41B1B936 for ; Thu, 20 Dec 2018 05:46:51 +0100 (CET) X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 19 Dec 2018 20:46:51 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,375,1539673200"; d="scan'208";a="260911811" Received: from dpdk-tbie.sh.intel.com ([10.67.104.173]) by orsmga004.jf.intel.com with ESMTP; 19 Dec 2018 20:46:49 -0800 Date: Thu, 20 Dec 2018 12:44:46 +0800 From: Tiwei Bie To: Maxime Coquelin Cc: dev@dpdk.org, i.maximets@samsung.com, zhihong.wang@intel.com, jfreiman@redhat.com, mst@redhat.com Message-ID: <20181220044446.GB21484@dpdk-tbie.sh.intel.com> References: <20181219092952.25728-1-maxime.coquelin@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181219092952.25728-1-maxime.coquelin@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) 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 04:46:52 -0000 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); > } > -- > 2.17.2 >