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Date: Mon, 14 Apr 2014 16:31:11 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Steven Galgano <sgalgano@...acentlink.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 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?
> 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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