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

Greg Kroah-Hartman
2015-01-25T19:01:54Z

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",