Patch "xen/netback: set default upper limit of tx/rx queues to 8" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

xen/netback: set default upper limit of tx/rx queues to 8

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xen-netback-set-default-upper-limit-of-tx-rx-queues-to-8.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Juergen Gross <[email protected]>
Date: Tue, 10 Jan 2017 14:32:52 +0100
Subject: xen/netback: set default upper limit of tx/rx queues to 8

From: Juergen Gross <[email protected]>

[ Upstream commit 56dd5af9bc23d0d5d23bb207c477715b4c2216c5 ]

The default for the maximum number of tx/rx queues of one interface is the number of cpus of the system today. As each queue pair reserves 512 grant pages this default consumes a ridiculous number of grants for large guests.

Limit the queue number to 8 as default. This value can be modified via a module parameter if required.

---
 drivers/net/xen-netback/netback.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -67,6 +67,7 @@ module_param(rx_drain_timeout_msecs, uin
 unsigned int rx_stall_timeout_msecs = 60000;
 module_param(rx_stall_timeout_msecs, uint, 0444);
 
+#define MAX_QUEUES_DEFAULT 8
 unsigned int xenvif_max_queues;
 module_param_named(max_queues, xenvif_max_queues, uint, 0644);
 MODULE_PARM_DESC(max_queues,

@@ -2189,11 +2190,12 @@ static int __init netback_init(void)
 	if (!xen_domain())
 		return -ENODEV;
 
-	/* Allow as many queues as there are CPUs if user has not
+	/* Allow as many queues as there are CPUs but max. 8 if user has not
 	 * specified a value.
 	 */
 	if (xenvif_max_queues == 0)
-		xenvif_max_queues = num_online_cpus();
+		xenvif_max_queues = min_t(unsigned int, MAX_QUEUES_DEFAULT,
+					  num_online_cpus());
 
 	if (fatal_skb_slots < XEN_NETBK_LEGACY_SLOTS_MAX) {
 		pr_info("fatal_skb_slots too small (%d), bump it to XEN_NETBK_LEGACY_SLOTS_MAX (%d)\n",

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/xen-netback-set-default-upper-limit-of-tx-rx-queues-to-8.patch