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?
>>>>>> /* Kick guest if required. */ >>>>>> if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) >>>>>> eventfd_write((int)vq->callfd, 1); >>>>>> >>>>> -- >>>>> Regards, >>>>> Haifeng >>>> >> >> . >>
