From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by dpdk.org (Postfix) with ESMTP id 58842379B for ; Wed, 1 Jun 2016 08:02:42 +0200 (CEST) Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga102.fm.intel.com with ESMTP; 31 May 2016 23:02:41 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,399,1459839600"; d="scan'208";a="712036400" Received: from yliu-dev.sh.intel.com (HELO yliu-dev) ([10.239.67.162]) by FMSMGA003.fm.intel.com with ESMTP; 31 May 2016 23:02:40 -0700 Date: Wed, 1 Jun 2016 14:05:32 +0800 From: Yuanhan Liu To: "Xie, Huawei" Cc: "dev@dpdk.org" , "stephen@networkplumber.org" , "Ananyev, Konstantin" , "thomas.monjalon@6wind.com" Message-ID: <20160601060532.GK5641@yliu-dev.sh.intel.com> References: <1464106601-981-1-git-send-email-huawei.xie@intel.com> <20160530082258.GF5641@yliu-dev.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Subject: Re: [dpdk-dev] [PATCH] virtio: use volatile to get used->idx in the loop X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 01 Jun 2016 06:02:42 -0000 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