Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753544AbbK3JV6 (ORCPT ); Mon, 30 Nov 2015 04:21:58 -0500 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:57894 "EHLO e06smtp16.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753356AbbK3JVz (ORCPT ); Mon, 30 Nov 2015 04:21:55 -0500 X-IBM-Helo: d06dlp01.portsmouth.uk.ibm.com X-IBM-MailFrom: borntraeger@de.ibm.com X-IBM-RcptTo: kvm@vger.kernel.org;linux-kernel@vger.kernel.org;netdev@vger.kernel.org Subject: Re: [PATCH v2] vhost: replace % with & on data path To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org References: <1448874894-18398-1-git-send-email-mst@redhat.com> Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org From: Christian Borntraeger Message-ID: <565C152C.2010409@de.ibm.com> Date: Mon, 30 Nov 2015 10:21:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <1448874894-18398-1-git-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15113009-0025-0000-0000-000007FCD1F4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1952 Lines: 55 On 11/30/2015 10:15 AM, Michael S. Tsirkin wrote: > We know vring num is a power of 2, so use & > to mask the high bits. Makes a lot of sense and virtio_ring.c seems to use the same logic. Acked-by: Christian Borntraeger > > Signed-off-by: Michael S. Tsirkin > --- > > Changes from v1: drop an unrelated chunk > > drivers/vhost/vhost.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 080422f..ad2146a 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -1369,7 +1369,7 @@ 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(__get_user(ring_head, > - &vq->avail->ring[last_avail_idx % vq->num]))) { > + &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]); > @@ -1489,7 +1489,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq, > u16 old, new; > int start; > > - start = vq->last_used_idx % vq->num; > + start = vq->last_used_idx & (vq->num - 1); > used = vq->used->ring + start; > if (count == 1) { > if (__put_user(heads[0].id, &used->id)) { > @@ -1531,7 +1531,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads, > { > int start, n, r; > > - start = vq->last_used_idx % vq->num; > + start = vq->last_used_idx & (vq->num - 1); > n = vq->num - start; > if (n < count) { > r = __vhost_add_used_n(vq, heads, n); > -- 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/