Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752261Ab1EIFx4 (ORCPT ); Mon, 9 May 2011 01:53:56 -0400 Received: from ozlabs.org ([203.10.76.45]:39355 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751417Ab1EIFxy (ORCPT ); Mon, 9 May 2011 01:53:54 -0400 From: Rusty Russell To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Carsten Otte , Christian Borntraeger , linux390@de.ibm.com, Martin Schwidefsky , Heiko Carstens , Shirley Ma , lguest@lists.ozlabs.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, Krishna Kumar , Tom Lendacky , steved@us.ibm.com, habanero@linux.vnet.ibm.com Subject: Re: [PATCH 09/18] virtio: use avail_event index In-Reply-To: <8bba6a0a8eee17e741c5155b04ff1b1c9f34bf94.1304541919.git.mst@redhat.com> References: <8bba6a0a8eee17e741c5155b04ff1b1c9f34bf94.1304541919.git.mst@redhat.com> User-Agent: Notmuch/0.3.1 (http://notmuchmail.org) Emacs/23.1.1 (i686-pc-linux-gnu) Date: Mon, 09 May 2011 14:03:26 +0930 Message-ID: <874o54h4rt.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1858 Lines: 56 On Wed, 4 May 2011 23:51:47 +0300, "Michael S. Tsirkin" wrote: > Use the new avail_event feature to reduce the number > of exits from the guest. Figures here would be nice :) > @@ -228,6 +237,12 @@ add_head: > * new available array entries. */ > virtio_wmb(); > vq->vring.avail->idx++; > + /* If the driver never bothers to kick in a very long while, > + * avail index might wrap around. If that happens, invalidate > + * kicked_avail index we stored. TODO: make sure all drivers > + * kick at least once in 2^16 and remove this. */ > + if (unlikely(vq->vring.avail->idx == vq->kicked_avail)) > + vq->kicked_avail_valid = true; If they don't, they're already buggy. Simply do: WARN_ON(vq->vring.avail->idx == vq->kicked_avail); > +static bool vring_notify(struct vring_virtqueue *vq) > +{ > + u16 old, new; > + bool v; > + if (!vq->event) > + return !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY); > + > + v = vq->kicked_avail_valid; > + old = vq->kicked_avail; > + new = vq->kicked_avail = vq->vring.avail->idx; > + vq->kicked_avail_valid = true; > + if (unlikely(!v)) > + return true; This is the only place you actually used kicked_avail_valid. Is it possible to initialize it in such a way that you can remove this? > @@ -482,6 +517,8 @@ void vring_transport_features(struct virtio_device *vdev) > break; > case VIRTIO_RING_F_USED_EVENT_IDX: > break; > + case VIRTIO_RING_F_AVAIL_EVENT_IDX: > + break; > default: > /* We don't understand this bit. */ > clear_bit(i, vdev->features); Does this belong in a prior patch? Thanks, Rusty. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/