Re: [PATCH 3.18 007/183] xen-netback: support frontends without feature-rx-notify again

John
2015-01-25T21:12:45Z

David,

No objections. I've been using it in production and have not seen any
problems.

-John

On 1/25/2015 10:05 AM, Greg Kroah-Hartman wrote:
> 3.18-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: David Vrabel <david.vrabel@citrix.com>
>
> [ Upstram commit 26c0e102585d5a4d311f5d6eb7f524d288e7f6b7 ]
>
> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
> feature-rx-notify mandatory) incorrectly assumed that there were no
> frontends in use that did not support this feature. But the frontend
> driver in MiniOS does not and since this is used by (qemu) stubdoms,
> these stopped working.
>
> Netback sort of works as-is in this mode except:
>
> - If there are no Rx requests and the internal Rx queue fills, only
> the drain timeout will wake the thread. The default drain timeout
> of 10 s would give unacceptable pauses.
>
> - If an Rx stall was detected and the internal Rx queue is drained,
> then the Rx thread would never wake.
>
> Handle these two cases (when feature-rx-notify is disabled) by:
>
> - Reducing the drain timeout to 30 ms.
>
> - Disabling Rx stall detection.
>
> Reported-by: John <jw@nuclearfallout.net>
> Tested-by: John <jw@nuclearfallout.net>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> Reviewed-by: Wei Liu <wei.liu2@citrix.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> drivers/net/xen-netback/common.h | 4 +++-
> drivers/net/xen-netback/interface.c | 4 +++-
> drivers/net/xen-netback/netback.c | 27 ++++++++++++++-------------
> drivers/net/xen-netback/xenbus.c | 12 +++++++++---
> 4 files changed, 29 insertions(+), 18 deletions(-)
>
> --- a/drivers/net/xen-netback/common.h
> +++ b/drivers/net/xen-netback/common.h
> @@ -230,6 +230,8 @@ struct xenvif {
> */
> bool disabled;
> unsigned long status;
> + unsigned long drain_timeout;
> + unsigned long stall_timeout;
>
> /* Queues */
> struct xenvif_queue *queues;
> @@ -328,7 +330,7 @@ irqreturn_t xenvif_interrupt(int irq, vo
> extern bool separate_tx_rx_irq;
>
> extern unsigned int rx_drain_timeout_msecs;
> -extern unsigned int rx_drain_timeout_jiffies;
> +extern unsigned int rx_stall_timeout_msecs;
> extern unsigned int xenvif_max_queues;
>
> #ifdef CONFIG_DEBUG_FS
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -166,7 +166,7 @@ static int xenvif_start_xmit(struct sk_b
> goto drop;
>
> cb = XENVIF_RX_CB(skb);
> - cb->expires = jiffies + rx_drain_timeout_jiffies;
> + cb->expires = jiffies + vif->drain_timeout;
>
> xenvif_rx_queue_tail(queue, skb);
> xenvif_kick_thread(queue);
> @@ -414,6 +414,8 @@ struct xenvif *xenvif_alloc(struct devic
> vif->ip_csum = 1;
> vif->dev = dev;
> vif->disabled = false;
> + vif->drain_timeout = msecs_to_jiffies(rx_drain_timeout_msecs);
> + vif->stall_timeout = msecs_to_jiffies(rx_stall_timeout_msecs);
>
> /* Start out with no queues. */
> vif->queues = NULL;
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -60,14 +60,12 @@ module_param(separate_tx_rx_irq, bool, 0
> */
> unsigned int rx_drain_timeout_msecs = 10000;
> module_param(rx_drain_timeout_msecs, uint, 0444);
> -unsigned int rx_drain_timeout_jiffies;
>
> /* The length of time before the frontend is considered unresponsive
> * because it isn't providing Rx slots.
> */
> -static unsigned int rx_stall_timeout_msecs = 60000;
> +unsigned int rx_stall_timeout_msecs = 60000;
> module_param(rx_stall_timeout_msecs, uint, 0444);
> -static unsigned int rx_stall_timeout_jiffies;
>
> unsigned int xenvif_max_queues;
> module_param_named(max_queues, xenvif_max_queues, uint, 0644);
> @@ -2022,7 +2020,7 @@ static bool xenvif_rx_queue_stalled(stru
> return !queue->stalled
> && prod - cons < XEN_NETBK_RX_SLOTS_MAX
> && time_after(jiffies,
> - queue->last_rx_time + rx_stall_timeout_jiffies);
> + queue->last_rx_time + queue->vif->stall_timeout);
> }
>
> static bool xenvif_rx_queue_ready(struct xenvif_queue *queue)
> @@ -2040,8 +2038,9 @@ static bool xenvif_have_rx_work(struct x
> {
> return (!skb_queue_empty(&queue->rx_queue)
> && xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX))
> - || xenvif_rx_queue_stalled(queue)
> - || xenvif_rx_queue_ready(queue)
> + || (queue->vif->stall_timeout &&
> + (xenvif_rx_queue_stalled(queue)
> + || xenvif_rx_queue_ready(queue)))
> || kthread_should_stop()
> || queue->vif->disabled;
> }
> @@ -2094,6 +2093,9 @@ int xenvif_kthread_guest_rx(void *data)
> struct xenvif_queue *queue = data;
> struct xenvif *vif = queue->vif;
>
> + if (!vif->stall_timeout)
> + xenvif_queue_carrier_on(queue);
> +
> for (;;) {
> xenvif_wait_for_rx_work(queue);
>
> @@ -2120,10 +2122,12 @@ int xenvif_kthread_guest_rx(void *data)
> * while it's probably not responsive, drop the
> * carrier so packets are dropped earlier.
> */
> - if (xenvif_rx_queue_stalled(queue))
> - xenvif_queue_carrier_off(queue);
> - else if (xenvif_rx_queue_ready(queue))
> - xenvif_queue_carrier_on(queue);
> + if (vif->stall_timeout) {
> + if (xenvif_rx_queue_stalled(queue))
> + xenvif_queue_carrier_off(queue);
> + else if (xenvif_rx_queue_ready(queue))
> + xenvif_queue_carrier_on(queue);
> + }
>
> /* Queued packets may have foreign pages from other
> * domains. These cannot be queued indefinitely as
> @@ -2194,9 +2198,6 @@ static int __init netback_init(void)
> if (rc)
> goto failed_init;
>
> - rx_drain_timeout_jiffies = msecs_to_jiffies(rx_drain_timeout_msecs);
> - rx_stall_timeout_jiffies = msecs_to_jiffies(rx_stall_timeout_msecs);
> -
> #ifdef CONFIG_DEBUG_FS
> xen_netback_dbg_root = debugfs_create_dir("xen-netback", NULL);
> if (IS_ERR_OR_NULL(xen_netback_dbg_root))
> --- a/drivers/net/xen-netback/xenbus.c
> +++ b/drivers/net/xen-netback/xenbus.c
> @@ -886,9 +886,15 @@ static int read_xenbus_vif_flags(struct
> return -EOPNOTSUPP;
>
> if (xenbus_scanf(XBT_NIL, dev->otherend,
> - "feature-rx-notify", "%d", &val) < 0 || val == 0) {
> - xenbus_dev_fatal(dev, -EINVAL, "feature-rx-notify is mandatory");
> - return -EINVAL;
> + "feature-rx-notify", "%d", &val) < 0)
> + val = 0;
> + if (!val) {
> + /* - Reduce drain timeout to poll more frequently for
> + * Rx requests.
> + * - Disable Rx stall detection.
> + */
> + be->vif->drain_timeout = msecs_to_jiffies(30);
> + be->vif->stall_timeout = 0;
> }
>
> if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-sg",
>
>