From: "Xie, Huawei" <huawei.xie@intel.com> To: Linhaifeng <haifeng.lin@huawei.com> Cc: "dev@dpdk.org" <dev@dpdk.org> Subject: Re: [dpdk-dev] [PATCH] cast used->idx to volatile Date: Tue, 24 Mar 2015 10:06:54 +0000 Message-ID: <C37D651A908B024F974696C65296B57B0F3F4DDD@SHSMSX101.ccr.corp.intel.com> (raw) In-Reply-To: <551115A9.8060106@huawei.com> 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@huawei.com] >>>>> Sent: Monday, March 23, 2015 8:24 PM >>>>> To: dev@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@huawei.com> >>>>>> >>>>>> Same as rte_vhost_enqueue_burst we should cast used->idx >>>>>> to volatile before notify guest. >>>>>> >>>>>> Signed-off-by: Linhaifeng <haifeng.lin@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 >>>> >> >> . >>
next prev parent reply other threads:[~2015-03-24 10:07 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-03-21 8:07 linhaifeng 2015-03-23 2:29 ` Linhaifeng 2015-03-23 12:23 ` Linhaifeng 2015-03-23 12:54 ` Xie, Huawei 2015-03-24 0:59 ` Linhaifeng 2015-03-24 1:53 ` Xie, Huawei 2015-03-24 7:43 ` Linhaifeng 2015-03-24 10:06 ` Xie, Huawei [this message] 2015-03-24 12:28 ` Linhaifeng 2015-03-30 9:20 ` Linhaifeng 2015-03-30 15:56 ` Xie, Huawei 2015-04-01 7:50 ` Thomas Monjalon 2015-04-01 14:40 ` Xie, Huawei
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