On 2015/3/24 18:06, Xie, Huawei wrote: > On 3/24/2015 3:44 PM, Linhaifeng wrote: >> >> 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? > I checked the code. Seems we can remove. That is another issue. > For your issue, you meet problem, and submit this this patch, but i am a > bit confused it is the root cause. Do you check the asm code that > volatile is optimized?
I'm not sure about this too.How to check volatile is optimized? > >>>>>>> /* Kick guest if required. */ >>>>>>> if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) >>>>>>> eventfd_write((int)vq->callfd, 1); >>>>>>> >>>>>> -- >>>>>> Regards, >>>>>> Haifeng >>>>> >>> >>> . >>> > > > . > -- Regards, Haifeng
