From patchwork Wed May 26 19:50:38 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Michael S. Tsirkin" X-Patchwork-Id: 53662 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [199.232.76.165]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 47648B7D1E for ; Thu, 27 May 2010 07:05:02 +1000 (EST) Received: from localhost ([127.0.0.1]:57177 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OHNmc-0006gz-Pu for incoming@patchwork.ozlabs.org; Wed, 26 May 2010 17:04:58 -0400 Received: from [140.186.70.92] (port=42596 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OHMhR-0007Or-Tw for qemu-devel@nongnu.org; Wed, 26 May 2010 15:55:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OHMhK-0004s0-4F for qemu-devel@nongnu.org; Wed, 26 May 2010 15:55:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60343) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OHMhJ-0004rg-Q5 for qemu-devel@nongnu.org; Wed, 26 May 2010 15:55:26 -0400 Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o4QJsrsG028137 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Wed, 26 May 2010 15:54:54 -0400 Received: from redhat.com (vpn-6-108.tlv.redhat.com [10.35.6.108]) by int-mx03.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with SMTP id o4QJspg5030751; Wed, 26 May 2010 15:54:52 -0400 Date: Wed, 26 May 2010 22:50:38 +0300 From: "Michael S. Tsirkin" To: Rusty Russell , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, qemu-devel@nongnu.org Message-ID: <8a6f96c73a72f04ed7c142e631ca59ee45b4b23b.1274903330.git.mst@redhat.com> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Mutt-Fcc: =sent User-Agent: Mutt/1.5.19 (2009-01-05) X-Scanned-By: MIMEDefang 2.67 on 10.5.11.16 X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. Cc: Subject: [Qemu-devel] [PATCHv2-RFC 1/2] virtio: support layout with avail ring before idx X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org This adds an (unused) option to put available ring before control (avail index, flags). This avoids cache line sharing between control and ring, and also makes it possible to extend avail control without incurring extra cache misses. Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_ring.c | 4 ++-- include/linux/virtio_ring.h | 30 ++++++++++++++++++++++++------ 2 files changed, 26 insertions(+), 8 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 1ca8890..2241342 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -224,7 +224,7 @@ add_head: /* Put entry in available array (but don't update avail->idx until they * do sync). FIXME: avoid modulus here? */ avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num; - vq->vring.avail->ring[avail] = head; + vq->vring.avail_ring[avail] = head; pr_debug("Added buffer head %i to %p\n", head, vq); END_USE(vq); @@ -425,7 +425,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int num, if (!vq) return NULL; - vring_init(&vq->vring, num, pages, vring_align); + vring_init(&vq->vring, num, pages, vring_align, false); vq->vq.callback = callback; vq->vq.vdev = vdev; vq->vq.name = name; diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index e4d144b..c5f3ee7 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -47,6 +47,11 @@ struct vring_avail { __u16 ring[]; }; +struct vring_avail_ctrl { + __u16 flags; + __u16 idx; +}; + /* u32 is used here for ids for padding reasons. */ struct vring_used_elem { /* Index of start of used descriptor chain. */ @@ -66,7 +71,9 @@ struct vring { struct vring_desc *desc; - struct vring_avail *avail; + struct vring_avail_ctrl *avail; + + __u16 *avail_ring; struct vring_used *used; }; @@ -79,11 +86,18 @@ struct vring { * // The actual descriptors (16 bytes each) * struct vring_desc desc[num]; * - * // A ring of available descriptor heads with free-running index. + * // A ring of available descriptor heads with a control structure + * // including a free-running index. + * // The ring can come either after (legacy) or before the control. * __u16 avail_flags; * __u16 avail_idx; * __u16 available[num]; * + * or + * + * __u16 available[num]; + * __u16 avail_flags; + * __u16 avail_idx; * // Padding to the next align boundary. * char pad[]; * @@ -94,13 +108,17 @@ struct vring { * }; */ static inline void vring_init(struct vring *vr, unsigned int num, void *p, - unsigned long align) + unsigned long align, bool avail_ring_first) { + struct vring_avail *avail = p + num * sizeof(struct vring_desc); vr->num = num; vr->desc = p; - vr->avail = p + num*sizeof(struct vring_desc); - vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + align-1) - & ~(align - 1)); + vr->avail_ring = avail_ring_first ? (void*)avail : &avail->ring; + vr->avail = avail_ring_first ? (void *)&vr->avail_ring[num] : p; + vr->used = (void *)ALIGN((unsigned long)&avail->ring[num], align); + /* Verify that avail fits before used. */ + BUG_ON((unsigned long)(vr->avail + 1) > (unsigned long)vr->used); + BUG_ON((unsigned long)(&vr->avail_ring[num]) > (unsigned long)vr->used); } static inline unsigned vring_size(unsigned int num, unsigned long align)