On 2015/3/23 20:54, Xie, Huawei wrote: > > >> -----Original Message----- >> From: Linhaifeng [mailto:haifeng.lin at huawei.com] >> Sent: Monday, March 23, 2015 8:24 PM >> To: dev at dpdk.org >> Cc: Ouyang, Changchun; Xie, Huawei >> Subject: Re: [dpdk-dev] [PATCH] cast used->idx to volatile >> >> >> >> On 2015/3/21 16:07, linhaifeng wrote: >>> From: Linhaifeng <haifeng.lin at huawei.com> >>> >>> Same as rte_vhost_enqueue_burst we should cast used->idx >>> to volatile before notify guest. >>> >>> Signed-off-by: Linhaifeng <haifeng.lin at huawei.com> >>> --- >>> lib/librte_vhost/vhost_rxtx.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c >>> index 535c7a1..8d674d1 100644 >>> --- a/lib/librte_vhost/vhost_rxtx.c >>> +++ b/lib/librte_vhost/vhost_rxtx.c >>> @@ -722,7 +722,7 @@ rte_vhost_dequeue_burst(struct virtio_net *dev, >> uint16_t queue_id, >>> } >>> >>> rte_compiler_barrier(); >>> - vq->used->idx += entry_success; >>> + *(volatile uint16_t *)&vq->used->idx += entry_success; > > > Haifeng: > We have compiler barrier before and an external function call behind, so we > don't need volatile here. > Do you meet issue? >
Tx_q is sometimes stopped when we use virtio_net. Because vhost thought there are no buffers in tx_q and virtio_net though vhost haven't handle all packets so we have to restart VM to restore work. The status in VM is: Mar 18 17:11:10 linux-b2ij kernel: [46337.246687] net eth7: virtnet_poll Mar 18 17:11:10 linux-b2ij kernel: [46337.246690] net eth7: receive_buf Mar 18 17:11:10 linux-b2ij kernel: [46337.246693] net eth7: vi->num=239 Mar 18 17:11:10 linux-b2ij kernel: [46337.246695] net eth7: svq:avail->idx=52939 used->idx=52939 num_free=18 num_added=0 svq->last_used_idx=52820 Mar 18 17:11:10 linux-b2ij kernel: [46337.246699] net eth7: rvq:avail->idx=36215 used->idx=35977 num_free=18 num_added=0 rvq->last_used_idx=35977 Mar 18 17:11:11 linux-b2ij kernel: [46337.901038] net eth7: dev_queue_xmit, qdisc->flags=4, qdisc->state deactiveed=0 Mar 18 17:11:12 linux-b2ij kernel: [46337.901042] net eth7: dev_queue_xmit, txq->state=1, stopped=1 Why compiler barrier not take effect in our case? Is compiler barrier depended on -O3 option? We use -O2 option. >>> /* Kick guest if required. */ >>> if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) >>> eventfd_write((int)vq->callfd, 1); >>> >> >> -- >> Regards, >> Haifeng > > > -- Regards, Haifeng
