From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yuanhan Liu Subject: Re: [PATCH] virtio: use volatile to get used->idx in the loop Date: Tue, 14 Jun 2016 21:23:38 +0800 Message-ID: <20160614132338.GB10038@yliu-dev.sh.intel.com> References: <1464106601-981-1-git-send-email-huawei.xie@intel.com> <20160530082258.GF5641@yliu-dev.sh.intel.com> <20160601060532.GK5641@yliu-dev.sh.intel.com> <20160602085215.GU10038@yliu-dev.sh.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "dev@dpdk.org" , "stephen@networkplumber.org" , "Ananyev, Konstantin" , "thomas.monjalon@6wind.com" To: "Xie, Huawei" Return-path: Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by dpdk.org (Postfix) with ESMTP id 1E0336CD3 for ; Tue, 14 Jun 2016 15:21:29 +0200 (CEST) Content-Disposition: inline In-Reply-To: List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Thu, Jun 02, 2016 at 08:54:38AM +0000, Xie, Huawei wrote: > On 6/2/2016 4:52 PM, Yuanhan Liu wrote: > > On Thu, Jun 02, 2016 at 08:39:36AM +0000, Xie, Huawei wrote: > >> On 6/1/2016 2:03 PM, Yuanhan Liu wrote: > >>> On Wed, Jun 01, 2016 at 05:40:08AM +0000, Xie, Huawei wrote: > >>>> On 5/30/2016 4:20 PM, Yuanhan Liu wrote: > >>>>> On Wed, May 25, 2016 at 12:16:41AM +0800, Huawei Xie wrote: > >>>>>> There is no external function call or any barrier in the loop, > >>>>>> the used->idx would only be retrieved once. > >>>>>> > >>>>>> Signed-off-by: Huawei Xie > >>>>>> --- > >>>>>> drivers/net/virtio/virtio_ethdev.c | 3 ++- > >>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > >>>>>> > >>>>>> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c > >>>>>> index c3fb628..f6d6305 100644 > >>>>>> --- a/drivers/net/virtio/virtio_ethdev.c > >>>>>> +++ b/drivers/net/virtio/virtio_ethdev.c > >>>>>> @@ -204,7 +204,8 @@ virtio_send_command(struct virtqueue *vq, struct virtio_pmd_ctrl *ctrl, > >>>>>> usleep(100); > >>>>>> } > >>>>>> > >>>>>> - while (vq->vq_used_cons_idx != vq->vq_ring.used->idx) { > >>>>>> + while (vq->vq_used_cons_idx != > >>>>>> + *((volatile uint16_t *)(&vq->vq_ring.used->idx))) { > >>>>> I'm wondering maybe we could fix VIRTQUEUE_NUSED (which has no such > >>>>> qualifier) and use this macro here? > >>>>> > >>>>> If you check the reference of that macro, you might find similar > >>>>> issues, say, it is also used inside the while-loop of > >>>>> virtio_recv_mergeable_pkts(). > >>>>> > >>>>> --yliu > >>>>> > >>>>> > >>>> Yes, seems it has same issue though haven't confirmed with asm code. > >>> So, move the "volatile" qualifier to VIRTQUEUE_NUSED? > >>> > >>> --yliu > >>> > >> Yes, anyway this is just intermediate fix. In next patch, will declare > >> the idx as volatile, and remove the qualifier in the macro. > > Hmm.., why we need an intermediate fix then, if we can come up with an > > ultimate fix very quickly? > > > > --yliu > > > ... Either is OK. I have no preference. Mind to send an ultimate fix then? --yliu