From patchwork Thu May 27 13:59:45 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: 102694 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by demeter.kernel.org (8.14.3/8.14.3) with ESMTP id o4RE537j006923 for ; Thu, 27 May 2010 14:05:03 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754143Ab0E0OEg (ORCPT ); Thu, 27 May 2010 10:04:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:9408 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752061Ab0E0OEf (ORCPT ); Thu, 27 May 2010 10:04:35 -0400 Received: from int-mx08.intmail.prod.int.phx2.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o4RE40NR008182 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 27 May 2010 10:04:01 -0400 Received: from redhat.com (vpn-6-107.tlv.redhat.com [10.35.6.107]) by int-mx08.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with SMTP id o4RE3vu3018566; Thu, 27 May 2010 10:03:58 -0400 Date: Thu, 27 May 2010 16:59:45 +0300 From: "Michael S. Tsirkin" To: Avi Kivity Cc: Rusty Russell , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, qemu-devel@nongnu.org Subject: Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself Message-ID: <20100527135945.GA8231@redhat.com> References: <4BFE6098.9010000@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4BFE6098.9010000@redhat.com> User-Agent: Mutt/1.5.19 (2009-01-05) X-Scanned-By: MIMEDefang 2.67 on 10.5.11.21 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by milter-greylist-4.2.3 (demeter.kernel.org [140.211.167.41]); Thu, 27 May 2010 14:05:04 +0000 (UTC) diff --git a/virtio-spec.lyx b/virtio-spec.lyx index ed35893..150e5a8 100644 --- a/virtio-spec.lyx +++ b/virtio-spec.lyx @@ -1803,6 +1803,36 @@ next \emph default descriptor entry (modulo the ring size). This starts at 0, and increases. +\change_inserted 0 1274966643 + +\end_layout + +\begin_layout Standard + +\change_inserted 0 1274968378 +When PUBLISH_USED feature flag has +\emph on +not +\emph default + been negotiated, the ring follows the +\begin_inset Quotes eld +\end_inset + +flags +\begin_inset Quotes erd +\end_inset + + and the +\begin_inset Quotes eld +\end_inset + +idx +\begin_inset Quotes erd +\end_inset + + fields: +\change_unchanged + \end_layout \begin_layout Standard @@ -1845,7 +1875,134 @@ struct vring_avail { \end_layout +\begin_layout Standard + +\change_inserted 0 1274968432 +\begin_inset CommandInset label +LatexCommand label +name "PUBLISH_USED-feature" + +\end_inset + +When PUBLISH_USED feature flag has been negotiated, the control structure + including the +\begin_inset Quotes eld +\end_inset + +flags and the +\begin_inset Quotes eld +\end_inset + +idx +\begin_inset Quotes erd +\end_inset + + fields follows the ring. + This leaves the room for the +\begin_inset Quotes eld +\end_inset + +last_seen_used_idx +\begin_inset Quotes erd +\end_inset + + field, which indicates the most recent +\begin_inset Quotes eld +\end_inset + +idx +\begin_inset Quotes erd +\end_inset + + value observed by guest in the used ring (see +\begin_inset CommandInset ref +LatexCommand ref +reference "sub:Used-Ring" + +\end_inset + + below): +\end_layout + +\begin_layout Standard + +\change_inserted 0 1274967396 +\begin_inset listings +inline false +status open + +\begin_layout Plain Layout + +\change_inserted 0 1274967404 + +struct vring_avail { +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274967405 + + u16 ring[qsz]; /* qsz is the Queue Size field read from device */ +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274967533 + +#define VRING_AVAIL_F_NO_INTERRUPT 1 +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274967533 + + u16 flags; +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274967533 + + u16 idx; +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274968345 + + u16 last_seen_used_idx; +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274967396 + +}; +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard + +\change_inserted 0 1274967715 +If the ring is large enough, the second layout maintains the control and + ring structures on separate cache lines. +\end_layout + \begin_layout Subsection + +\change_inserted 0 1274968415 +\begin_inset CommandInset label +LatexCommand label +name "sub:Used-Ring" + +\end_inset + + +\change_unchanged Used Ring \end_layout @@ -2391,12 +2548,20 @@ status open \begin_layout Plain Layout -while (vq->last_seen_used != vring->used.idx) { +while (vq->last_seen_used +\change_inserted 0 1274968316 +_idx +\change_unchanged + != vring->used.idx) { \end_layout \begin_layout Plain Layout - struct vring_used_elem *e = vring.used->ring[vq->last_seen_used%vsz]; + struct vring_used_elem *e = vring.used->ring[vq->last_seen_used +\change_inserted 0 1274968326 +_idx +\change_unchanged +%vsz]; \end_layout \begin_layout Plain Layout @@ -2406,7 +2571,11 @@ while (vq->last_seen_used != vring->used.idx) { \begin_layout Plain Layout - vq->last_seen_used++; + vq->last_seen_used +\change_inserted 0 1274968321 +_idx +\change_unchanged +++; \end_layout \begin_layout Plain Layout @@ -2419,6 +2588,13 @@ while (vq->last_seen_used != vring->used.idx) { \end_layout +\begin_layout Standard + +\change_inserted 0 1274968252 +If PUBLISH_USED feature is negotiated, last_seen_used value should be published + to the device in the avail ring. +\end_layout + \begin_layout Subsection Dealing With Configuration Changes \end_layout @@ -2986,6 +3162,47 @@ struct vring_avail { \begin_layout Plain Layout }; +\change_inserted 0 1274966477 + +\end_layout + +\begin_layout Plain Layout + +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274966484 + +struct vring_avail_ctrl { +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274966489 + + __u16 flags; +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274966494 + + __u16 idx; +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274966499 + + __u16 last_used_idx; +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1274966474 + +}; \end_layout \begin_layout Plain Layout @@ -3349,6 +3566,28 @@ reference "sub:Indirect-Descriptors" \end_inset . +\change_inserted 0 1274967762 + +\end_layout + +\begin_layout Description + +\change_inserted 0 1274967926 +VIRTIO_F_RING_PUBLISH_USED +\begin_inset space ~ +\end_inset + +(29) Negotiating this feature indicates that the avail ring layout includes + the used index observed by driver, see +\begin_inset CommandInset ref +LatexCommand ref +reference "PUBLISH_USED-feature" + +\end_inset + +. +\change_unchanged + \end_layout \begin_layout Description