On 2015/3/24 9:53, Xie, Huawei wrote: > On 3/24/2015 9:00 AM, Linhaifeng wrote: >> >> 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. > compiler barrier always works regardless of the optimization option. > I don't get your story, but the key thing is, do you check the asm code? > If called from outside as an API, how is it possible it is optimized? > there is only one update to used->idx in that function.
Do you mean rte_vhost_enqueue_burst also not need cast used->idx to volatile ? Why not remove it? >> >>>>> /* Kick guest if required. */ >>>>> if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) >>>>> eventfd_write((int)vq->callfd, 1); >>>>> >>>> -- >>>> Regards, >>>> Haifeng >>> >>> > > > . > -- Regards, Haifeng
