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Date: Mon, 14 Apr 2014 09:43:44 -0400
From: Steven Galgano <sgalgano@...acentlink.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: David Miller <davem@...emloft.net>, jasowang@...hat.com,
xemul@...allels.com, wuzhy@...ux.vnet.ibm.com, therbert@...gle.com,
yamato@...hat.com, richardcochran@...il.com,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
Brian.Adamson@....navy.mil, jgiovatto@...acentlink.com
Subject: Re: [PATCH v3] tuntap: add flow control to support back pressure
On 04/14/2014 09:31 AM, Michael S. Tsirkin wrote:
> On Mon, Apr 14, 2014 at 09:21:47AM -0400, Steven Galgano wrote:
>> Added optional per queue flow control support using IFF_FLOW_CONTROL. When the
>> IFF_FLOW_CONTROL TUNSETIFF flag is specified it will set a per queue flag to
>> indicate that the queue should be stopped using netif_tx_stop_queue(), rather
>> than discarding frames once full. After reading a frame from the respective
>> stopped queue, a netif_tx_wake_queue() is issued to signal resource
>> availability.
>>
>> The per queue TUN_FLOW_CONTROL flag is stored in struct tun_file. This provides
>> the flexibility to enable flow control on all, none or some queues when using
>> IFF_MULTI_QUEUE. When not using IFF_MULTI_QUEUE, IFF_FLOW_CONTROL will apply to
>> the single queue. No changes were made to the default drop frame policy.
>>
>> This change adds support for back pressure use cases.
>>
>> Reported-by: Brian Adamson <brian.adamson@....navy.mil>
>> Tested-by: Joseph Giovatto <jgiovatto@...acentlink.com>
>> Signed-off-by: Steven Galgano <sgalgano@...acentlink.com>
>> ---
>> Version 3 patch reformatted commit message to be 80 columns max width.
>> Corrected Tested-By email address.
>> Version 2 patch added support for individual queues when applying flow
>> control instead of using netif_tx_stop_all_queues()/netif_tx_wake_all_queues().
>
> Any plans to try and address the more material comments on v2?
>
Yes. My apologies, I missed your response.
>> drivers/net/tun.c | 32 ++++++++++++++++++++++++++++----
>> include/uapi/linux/if_tun.h | 2 ++
>> 2 files changed, 30 insertions(+), 4 deletions(-)
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index ee328ba..3d09f5a 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -137,7 +137,7 @@ struct tun_file {
>> struct tun_struct __rcu *tun;
>> struct net *net;
>> struct fasync_struct *fasync;
>> - /* only used for fasnyc */
>> + /* used for fasnyc and flow control */
>> unsigned int flags;
>> union {
>> u16 queue_index;
>> @@ -783,8 +783,19 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>> * number of queues.
>> */
>> if (skb_queue_len(&tfile->socket.sk->sk_receive_queue) * numqueues
>> - >= dev->tx_queue_len)
>> - goto drop;
>> + >= dev->tx_queue_len) {
>> + if (tfile->flags & TUN_FLOW_CONTROL) {
>> + /* Resources unavailable stop queue */
>> + netif_tx_stop_queue(netdev_get_tx_queue(dev, txq));
>> +
>> + /* We won't see all dropped packets individually, so
>> + * over run error is more appropriate.
>> + */
>> + dev->stats.tx_fifo_errors++;
>> + } else {
>> + goto drop;
>> + }
>> + }
>>
>> if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
>> goto drop;
>> @@ -1333,6 +1344,7 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
>> DECLARE_WAITQUEUE(wait, current);
>> struct sk_buff *skb;
>> ssize_t ret = 0;
>> + struct netdev_queue *ntxq;
>>
>> tun_debug(KERN_INFO, tun, "tun_do_read\n");
>>
>> @@ -1362,6 +1374,12 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
>> continue;
>> }
>>
>> + ntxq = netdev_get_tx_queue(tun->dev, tfile->queue_index);
>> +
>> + if (tfile->flags & TUN_FLOW_CONTROL &&
>> + netif_tx_queue_stopped(ntxq))
>> + netif_tx_wake_queue(ntxq);
>> +
>> ret = tun_put_user(tun, tfile, skb, iv, len);
>> kfree_skb(skb);
>> break;
>> @@ -1732,6 +1750,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>> else
>> tun->flags &= ~TUN_TAP_MQ;
>>
>> + if (ifr->ifr_flags & IFF_FLOW_CONTROL)
>> + tfile->flags |= TUN_FLOW_CONTROL;
>> + else
>> + tfile->flags &= ~TUN_FLOW_CONTROL;
>> +
>> /* Make sure persistent devices do not get stuck in
>> * xoff state.
>> */
>> @@ -1900,7 +1923,8 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
>> * This is needed because we never checked for invalid flags on
>> * TUNSETIFF. */
>> return put_user(IFF_TUN | IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE |
>> - IFF_VNET_HDR | IFF_MULTI_QUEUE,
>> + IFF_VNET_HDR | IFF_MULTI_QUEUE |
>> + IFF_FLOW_CONTROL,
>> (unsigned int __user*)argp);
>> } else if (cmd == TUNSETQUEUE)
>> return tun_set_queue(file, &ifr);
>> diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
>> index e9502dd..bcf2790 100644
>> --- a/include/uapi/linux/if_tun.h
>> +++ b/include/uapi/linux/if_tun.h
>> @@ -36,6 +36,7 @@
>> #define TUN_PERSIST 0x0100
>> #define TUN_VNET_HDR 0x0200
>> #define TUN_TAP_MQ 0x0400
>> +#define TUN_FLOW_CONTROL 0x0800
>>
>> /* Ioctl defines */
>> #define TUNSETNOCSUM _IOW('T', 200, int)
>> @@ -70,6 +71,7 @@
>> #define IFF_MULTI_QUEUE 0x0100
>> #define IFF_ATTACH_QUEUE 0x0200
>> #define IFF_DETACH_QUEUE 0x0400
>> +#define IFF_FLOW_CONTROL 0x0010
>> /* read-only flag */
>> #define IFF_PERSIST 0x0800
>> #define IFF_NOFILTER 0x1000
--
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