From: "Xie, Huawei" <huawei.xie@intel.com>
To: Tom Kiely <tkiely@brocade.com>, "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] virtio: fix rx ring descriptor starvation
Date: Tue, 5 Jan 2016 07:13:04 +0000 [thread overview]
Message-ID: <C37D651A908B024F974696C65296B57B4C574D68@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <567299E9.60000@brocade.com>
On 12/17/2015 7:18 PM, Tom Kiely wrote:
>
>
> On 11/25/2015 05:32 PM, Xie, Huawei wrote:
>> On 11/13/2015 5:33 PM, Tom Kiely wrote:
>>> If all rx descriptors are processed while transient
>>> mbuf exhaustion is present, the rx ring ends up with
>>> no available descriptors. Thus no packets are received
>>> on that ring. Since descriptor refill is performed post
>>> rx descriptor processing, in this case no refill is
>>> ever subsequently performed resulting in permanent rx
>>> traffic drop.
>>>
>>> Signed-off-by: Tom Kiely <tkiely@brocade.com>
>>> ---
>>> drivers/net/virtio/virtio_rxtx.c | 6 ++++--
>>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio/virtio_rxtx.c
>>> b/drivers/net/virtio/virtio_rxtx.c
>>> index 5770fa2..a95e234 100644
>>> --- a/drivers/net/virtio/virtio_rxtx.c
>>> +++ b/drivers/net/virtio/virtio_rxtx.c
>>> @@ -586,7 +586,8 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf
>>> **rx_pkts, uint16_t nb_pkts)
>>> if (likely(num > DESC_PER_CACHELINE))
>>> num = num - ((rxvq->vq_used_cons_idx + num) %
>>> DESC_PER_CACHELINE);
>>> - if (num == 0)
>>> + /* Refill free descriptors even if no pkts recvd */
>>> + if (num == 0 && virtqueue_full(rxvq))
>> Should the return condition be that no used buffers and we have avail
>> descs in avail ring, i.e,
>> num == 0 && rxvq->vq_free_cnt != rxvq->vq_nentries
>>
>> rather than
>> num == 0 && rxvq->vq_free_cnt == 0
> Yes we could do that but I don't see a good reason to wait until the
> vq_free_cnt == vq_nentries
> before attempting the refill. The existing code will attempt refill
> even if only 1 packet was received
> and the free count is small. To me it seems safer to extend that to
> try refill even if no packet was received
> but the free count is non-zero.
The existing code attempt to refill only if 1 packet was received.
If we want to refill even no packet was received, then the strict
condition should be
num == 0 && rxvq->vq_free_cnt != rxvq->vq_nentries
The safer condition, what you want to use, should be
num == 0 && !virtqueue_full(...)
rather than
num == 0 && virtqueue_full(...)
We could simplify things a bit, just remove this check, if the following
receiving code already takes care of the "num == 0" condition.
I find virtqueue_full is confusing, maybe we could change it to some
other meaningful name.
>
> Tom
>
>>> return 0;
>>> num = virtqueue_dequeue_burst_rx(rxvq, rcv_pkts, len, num);
>>> @@ -683,7 +684,8 @@ virtio_recv_mergeable_pkts(void *rx_queue,
>>> virtio_rmb();
>>> - if (nb_used == 0)
>>> + /* Refill free descriptors even if no pkts recvd */
>>> + if (nb_used == 0 && virtqueue_full(rxvq))
>>> return 0;
>>> PMD_RX_LOG(DEBUG, "used:%d\n", nb_used);
>
>
next prev parent reply other threads:[~2016-01-05 7:13 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-13 9:30 Tom Kiely
2015-11-24 21:20 ` Thomas Monjalon
2015-11-25 1:50 ` Yuanhan Liu
2015-11-25 2:51 ` Xie, Huawei
2015-11-25 17:32 ` Xie, Huawei
[not found] ` <C37D651A908B024F974696C65296B57B4C545F75@SHSMSX101.ccr.corp.intel.com>
2015-12-17 9:22 ` Tom Kiely
2015-12-17 11:18 ` Tom Kiely
2016-01-05 7:13 ` Xie, Huawei [this message]
2016-02-10 15:07 ` Bruce Richardson
2016-02-18 14:03 ` Kyle Larose
2016-02-22 16:23 ` Tom Kiely
2016-02-23 8:26 ` Xie, Huawei
2016-03-04 6:16 ` Xie, Huawei
2016-03-04 8:11 ` Tom Kiely
2016-03-04 13:25 ` Kyle Larose
2016-03-09 21:37 ` Bruce Richardson
2016-03-10 14:46 ` Kyle Larose
2016-02-26 18:58 Kyle Larose
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