From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Xie, Huawei" Subject: Re: [PATCH] cast used->idx to volatile Date: Tue, 24 Mar 2015 01:53:56 +0000 Message-ID: References: <1426925237-8312-1-git-send-email-haifeng.lin@huawei.com> <551005DD.4060508@huawei.com> <5510B709.5030907@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Cc: "dev-VfR2kkLFssw@public.gmane.org" To: Linhaifeng Return-path: Content-Language: en-US List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces-VfR2kkLFssw@public.gmane.org Sender: "dev" On 3/24/2015 9:00 AM, Linhaifeng wrote:=0A= >=0A= > On 2015/3/23 20:54, Xie, Huawei wrote:=0A= >>=0A= >>> -----Original Message-----=0A= >>> From: Linhaifeng [mailto:haifeng.lin-hv44wF8Li93QT0dZR+AlfA@public.gmane.org]=0A= >>> Sent: Monday, March 23, 2015 8:24 PM=0A= >>> To: dev-VfR2kkLFssw@public.gmane.org=0A= >>> Cc: Ouyang, Changchun; Xie, Huawei=0A= >>> Subject: Re: [dpdk-dev] [PATCH] cast used->idx to volatile=0A= >>>=0A= >>>=0A= >>>=0A= >>> On 2015/3/21 16:07, linhaifeng wrote:=0A= >>>> From: Linhaifeng =0A= >>>>=0A= >>>> Same as rte_vhost_enqueue_burst we should cast used->idx=0A= >>>> to volatile before notify guest.=0A= >>>>=0A= >>>> Signed-off-by: Linhaifeng =0A= >>>> ---=0A= >>>> lib/librte_vhost/vhost_rxtx.c | 2 +-=0A= >>>> 1 file changed, 1 insertion(+), 1 deletion(-)=0A= >>>>=0A= >>>> diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rx= tx.c=0A= >>>> index 535c7a1..8d674d1 100644=0A= >>>> --- a/lib/librte_vhost/vhost_rxtx.c=0A= >>>> +++ b/lib/librte_vhost/vhost_rxtx.c=0A= >>>> @@ -722,7 +722,7 @@ rte_vhost_dequeue_burst(struct virtio_net *dev,=0A= >>> uint16_t queue_id,=0A= >>>> }=0A= >>>>=0A= >>>> rte_compiler_barrier();=0A= >>>> - vq->used->idx +=3D entry_success;=0A= >>>> + *(volatile uint16_t *)&vq->used->idx +=3D entry_success;=0A= >>=0A= >> Haifeng:=0A= >> We have compiler barrier before and an external function call behind, so= we don't need volatile here.=0A= >> Do you meet issue?=0A= >>=0A= > Tx_q is sometimes stopped when we use virtio_net. Because vhost thought t= here are no buffers in tx_q and virtio_net=0A= > though vhost haven't handle all packets so we have to restart VM to resto= re work.=0A= >=0A= > The status in VM is:=0A= > Mar 18 17:11:10 linux-b2ij kernel: [46337.246687] net eth7: virtnet_poll= =0A= > Mar 18 17:11:10 linux-b2ij kernel: [46337.246690] net eth7: receive_buf= =0A= > Mar 18 17:11:10 linux-b2ij kernel: [46337.246693] net eth7: vi->num=3D239= =0A= > Mar 18 17:11:10 linux-b2ij kernel: [46337.246695] net eth7: svq:avail->id= x=3D52939 used->idx=3D52939 num_free=3D18 num_added=3D0 svq->last_used_idx= =3D52820=0A= > Mar 18 17:11:10 linux-b2ij kernel: [46337.246699] net eth7: rvq:avail->id= x=3D36215 used->idx=3D35977 num_free=3D18 num_added=3D0 rvq->last_used_idx= =3D35977=0A= > Mar 18 17:11:11 linux-b2ij kernel: [46337.901038] net eth7: dev_queue_xmi= t, qdisc->flags=3D4, qdisc->state deactiveed=3D0=0A= > Mar 18 17:11:12 linux-b2ij kernel: [46337.901042] net eth7: dev_queue_xmi= t, txq->state=3D1, stopped=3D1=0A= >=0A= > Why compiler barrier not take effect in our case? Is compiler barrier dep= ended on -O3 option? We use -O2 option.=0A= compiler barrier always works regardless of the optimization option.=0A= I don't get your story, but the key thing is, do you check the asm code?=0A= If called from outside as an API, how is it possible it is optimized?=0A= there is only one update to used->idx in that function.=0A= >=0A= >>>> /* Kick guest if required. */=0A= >>>> if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))=0A= >>>> eventfd_write((int)vq->callfd, 1);=0A= >>>>=0A= >>> --=0A= >>> Regards,=0A= >>> Haifeng=0A= >>=0A= >>=0A= =0A=