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GET /api/patches/47232/?format=api
{ "id": 47232, "url": "https://patches.dpdk.org/api/patches/47232/?format=api", "web_url": "https://patches.dpdk.org/project/dpdk/patch/20181023100710.14739-1-maxime.coquelin@redhat.com/", "project": { "id": 1, "url": "https://patches.dpdk.org/api/projects/1/?format=api", "name": "DPDK", "link_name": "dpdk", "list_id": "dev.dpdk.org", "list_email": "dev@dpdk.org", "web_url": "http://core.dpdk.org", "scm_url": "git://dpdk.org/dpdk", "webscm_url": "http://git.dpdk.org/dpdk", "list_archive_url": "https://inbox.dpdk.org/dev", "list_archive_url_format": "https://inbox.dpdk.org/dev/{}", "commit_url_format": "" }, "msgid": "<20181023100710.14739-1-maxime.coquelin@redhat.com>", "list_archive_url": "https://inbox.dpdk.org/dev/20181023100710.14739-1-maxime.coquelin@redhat.com", "date": "2018-10-23T10:07:10", "name": "[v2] vhost: avoid memory barriers when no descriptors dequeued", "commit_ref": null, "pull_url": null, "state": "accepted", "archived": true, "hash": "634abc2457bb459fa57b970f4008bf3cec770c99", "submitter": { "id": 512, "url": "https://patches.dpdk.org/api/people/512/?format=api", "name": "Maxime Coquelin", "email": "maxime.coquelin@redhat.com" }, "delegate": { "id": 2642, "url": "https://patches.dpdk.org/api/users/2642/?format=api", "username": "mcoquelin", "first_name": "Maxime", "last_name": "Coquelin", "email": "maxime.coquelin@redhat.com" }, "mbox": "https://patches.dpdk.org/project/dpdk/patch/20181023100710.14739-1-maxime.coquelin@redhat.com/mbox/", "series": [ { "id": 2030, "url": "https://patches.dpdk.org/api/series/2030/?format=api", "web_url": "https://patches.dpdk.org/project/dpdk/list/?series=2030", "date": "2018-10-23T10:07:10", "name": "[v2] vhost: avoid memory barriers when no descriptors dequeued", "version": 2, "mbox": "https://patches.dpdk.org/series/2030/mbox/" } ], "comments": "https://patches.dpdk.org/api/patches/47232/comments/", "check": "success", "checks": "https://patches.dpdk.org/api/patches/47232/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<dev-bounces@dpdk.org>", "X-Original-To": "patchwork@dpdk.org", "Delivered-To": "patchwork@dpdk.org", "Received": [ "from [92.243.14.124] (localhost [127.0.0.1])\n\tby dpdk.org (Postfix) with ESMTP id 981771B4A1;\n\tTue, 23 Oct 2018 12:07:25 +0200 (CEST)", "from mx1.redhat.com (mx1.redhat.com [209.132.183.28])\n\tby dpdk.org (Postfix) with ESMTP id 469D71B49E;\n\tTue, 23 Oct 2018 12:07:20 +0200 (CEST)", "from smtp.corp.redhat.com\n\t(int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15])\n\t(using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))\n\t(No client certificate requested)\n\tby mx1.redhat.com (Postfix) with ESMTPS id 732B5C0587EE;\n\tTue, 23 Oct 2018 10:07:19 +0000 (UTC)", "from max-t460s.localdomain (ovpn-112-43.ams2.redhat.com\n\t[10.36.112.43])\n\tby smtp.corp.redhat.com (Postfix) with ESMTP id D543E5D6AA;\n\tTue, 23 Oct 2018 10:07:12 +0000 (UTC)" ], "From": "Maxime Coquelin <maxime.coquelin@redhat.com>", "To": "dev@dpdk.org, tiwei.bie@intel.com, jfreimann@redhat.com,\n\tzhihong.wang@intel.com", "Cc": "Maxime Coquelin <maxime.coquelin@redhat.com>,\n\tstable@dpdk.org", "Date": "Tue, 23 Oct 2018 12:07:10 +0200", "Message-Id": "<20181023100710.14739-1-maxime.coquelin@redhat.com>", "X-Scanned-By": "MIMEDefang 2.79 on 10.5.11.15", "X-Greylist": "Sender IP whitelisted, not delayed by milter-greylist-4.5.16\n\t(mx1.redhat.com [10.5.110.32]); Tue, 23 Oct 2018 10:07:19 +0000 (UTC)", "Subject": "[dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no\n\tdescriptors dequeued", "X-BeenThere": "dev@dpdk.org", "X-Mailman-Version": "2.1.15", "Precedence": "list", "List-Id": "DPDK patches and discussions <dev.dpdk.org>", "List-Unsubscribe": "<https://mails.dpdk.org/options/dev>,\n\t<mailto:dev-request@dpdk.org?subject=unsubscribe>", "List-Archive": "<http://mails.dpdk.org/archives/dev/>", "List-Post": "<mailto:dev@dpdk.org>", "List-Help": "<mailto:dev-request@dpdk.org?subject=help>", "List-Subscribe": "<https://mails.dpdk.org/listinfo/dev>,\n\t<mailto:dev-request@dpdk.org?subject=subscribe>", "Errors-To": "dev-bounces@dpdk.org", "Sender": "\"dev\" <dev-bounces@dpdk.org>" }, "content": "In both split and packed dequeue paths, flush_shadow_used_ring\nand vhost_ring_call variants gets called even if not packets\nhave been dequeued, and so no descriptors updates happened.\n\nIt has an impact on CPU pipeline, as memory barriers are used\nin these functions.\n\nThis patch don't call these functions if no descriptors have\nbeen dequeued. The performance gain with split ring when\ndequeue zero-copy is disabled should be null, but should be\nnoticeable with packed ring or dequeue zero-copy enabled.\n\nFixes: ae999ce49dcb (\"vhost: add Tx support for packed ring\")\nFixes: 915cf9404225 (\"vhost: use shadow used ring in dequeue path\")\nCc: stable@dpdk.org\n\nSigned-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>\n---\n\nChanges in v2:\n- Fix shadow_used_idx reset in error path (Tiwei)\n\n lib/librte_vhost/virtio_net.c | 24 ++++++++++++++++--------\n 1 file changed, 16 insertions(+), 8 deletions(-)", "diff": "diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c\nindex 1c31c0562..8ad30c94a 100644\n--- a/lib/librte_vhost/virtio_net.c\n+++ b/lib/librte_vhost/virtio_net.c\n@@ -1360,8 +1360,10 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,\n \t\t\t}\n \t\t}\n \n-\t\tflush_shadow_used_ring_split(dev, vq);\n-\t\tvhost_vring_call_split(dev, vq);\n+\t\tif (likely(vq->shadow_used_idx)) {\n+\t\t\tflush_shadow_used_ring_split(dev, vq);\n+\t\t\tvhost_vring_call_split(dev, vq);\n+\t\t}\n \t}\n \n \trte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);\n@@ -1440,8 +1442,10 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,\n \t\tdo_data_copy_dequeue(vq);\n \t\tif (unlikely(i < count))\n \t\t\tvq->shadow_used_idx = i;\n-\t\tflush_shadow_used_ring_split(dev, vq);\n-\t\tvhost_vring_call_split(dev, vq);\n+\t\tif (likely(vq->shadow_used_idx)) {\n+\t\t\tflush_shadow_used_ring_split(dev, vq);\n+\t\t\tvhost_vring_call_split(dev, vq);\n+\t\t}\n \t}\n \n \treturn i;\n@@ -1476,8 +1480,10 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,\n \t\t\t}\n \t\t}\n \n-\t\tflush_shadow_used_ring_packed(dev, vq);\n-\t\tvhost_vring_call_packed(dev, vq);\n+\t\tif (likely(vq->shadow_used_idx)) {\n+\t\t\tflush_shadow_used_ring_packed(dev, vq);\n+\t\t\tvhost_vring_call_packed(dev, vq);\n+\t\t}\n \t}\n \n \tVHOST_LOG_DEBUG(VHOST_DATA, \"(%d) %s\\n\", dev->vid, __func__);\n@@ -1555,8 +1561,10 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,\n \t\tdo_data_copy_dequeue(vq);\n \t\tif (unlikely(i < count))\n \t\t\tvq->shadow_used_idx = i;\n-\t\tflush_shadow_used_ring_packed(dev, vq);\n-\t\tvhost_vring_call_packed(dev, vq);\n+\t\tif (likely(vq->shadow_used_idx)) {\n+\t\t\tflush_shadow_used_ring_packed(dev, vq);\n+\t\t\tvhost_vring_call_packed(dev, vq);\n+\t\t}\n \t}\n \n \treturn i;\n", "prefixes": [ "v2" ] }