From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53B2EC43387 for ; Wed, 9 Jan 2019 08:05:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2978121726 for ; Wed, 9 Jan 2019 08:05:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729816AbfAIIF4 (ORCPT ); Wed, 9 Jan 2019 03:05:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49922 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729731AbfAIIFr (ORCPT ); Wed, 9 Jan 2019 03:05:47 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EE397C057E00; Wed, 9 Jan 2019 08:05:46 +0000 (UTC) Received: from jason-ThinkPad-T450s.redhat.com (ovpn-12-204.pek2.redhat.com [10.72.12.204]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7B9241A917; Wed, 9 Jan 2019 08:05:44 +0000 (UTC) From: Jason Wang To: mst@redhat.com, jasowang@redhat.com Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next V2 3/3] vhost: don't touch avail ring if in_order is negotiated Date: Wed, 9 Jan 2019 16:05:30 +0800 Message-Id: <20190109080530.18572-4-jasowang@redhat.com> In-Reply-To: <20190109080530.18572-1-jasowang@redhat.com> References: <20190109080530.18572-1-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Wed, 09 Jan 2019 08:05:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Device use descriptors table in order, so there's no need to read index from available ring. This eliminate the cache contention on available ring completely. Virito-user + vhost_kernel + XDP_DROP on 2.60GHz Broadwell Before /After SMAP on: 4.8Mpps 5.3Mpps(+10%) SMAP off: 6.6Mpps 7.0Mpps(+6%) Signed-off-by: Jason Wang --- drivers/vhost/vhost.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 55e5aa662ad5..ab0d05262235 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -2012,6 +2012,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, __virtio16 avail_idx; __virtio16 ring_head; int ret, access; + bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER); /* Check it isn't doing very strange things with descriptor numbers. */ last_avail_idx = vq->last_avail_idx; @@ -2044,15 +2045,19 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, /* Grab the next descriptor number they're advertising, and increment * the index we've seen. */ - if (unlikely(vhost_get_avail(vq, ring_head, - &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) { - vq_err(vq, "Failed to read head: idx %d address %p\n", - last_avail_idx, - &vq->avail->ring[last_avail_idx % vq->num]); - return -EFAULT; + if (!in_order) { + if (unlikely(vhost_get_avail(vq, ring_head, + &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) { + vq_err(vq, "Failed to read head: idx %d address %p\n", + last_avail_idx, + &vq->avail->ring[last_avail_idx % vq->num]); + return -EFAULT; + } + head = vhost16_to_cpu(vq, ring_head); + } else { + head = last_avail_idx & (vq->num - 1); } - head = vhost16_to_cpu(vq, ring_head); /* If their number is silly, that's an error. */ if (unlikely(head >= vq->num)) { -- 2.17.1