From: jbeulich@novell.com
Subject: allow number of guest devices to be configurable
Patch-mainline: obsolete

... and derive NR_DYNIRQS from this (rather than having a hard-coded
value).
Similarly, allow the number of simultaneous transmits in netback to be
configurable.

--- head-2010-04-15.orig/arch/x86/include/mach-xen/asm/irq_vectors.h	2010-03-30 17:15:14.000000000 +0200
+++ head-2010-04-15/arch/x86/include/mach-xen/asm/irq_vectors.h	2010-04-15 11:44:09.000000000 +0200
@@ -95,7 +95,7 @@ extern int nr_pirqs;
 #endif
 
 #define DYNIRQ_BASE			(PIRQ_BASE + nr_pirqs)
-#define NR_DYNIRQS			256
+#define NR_DYNIRQS			(64 + CONFIG_XEN_NR_GUEST_DEVICES)
 
 #define NR_IRQS				(NR_PIRQS + NR_DYNIRQS)
 
--- head-2010-04-15.orig/drivers/xen/Kconfig	2010-03-31 14:11:27.000000000 +0200
+++ head-2010-04-15/drivers/xen/Kconfig	2010-03-31 14:11:36.000000000 +0200
@@ -98,6 +98,15 @@ config XEN_NETDEV_BACKEND
 	  network devices to other guests via a high-performance shared-memory
 	  interface.
 
+config XEN_NETDEV_TX_SHIFT
+	int "Maximum simultaneous transmit requests (as a power of 2)"
+	depends on XEN_NETDEV_BACKEND
+	range 5 16
+	default 8
+	help
+	  The maximum number transmits the driver can hold pending, expressed
+	  as the exponent of a power of 2.
+
 config XEN_NETDEV_PIPELINED_TRANSMITTER
 	bool "Pipelined transmitter (DANGEROUS)"
 	depends on XEN_NETDEV_BACKEND
@@ -309,6 +318,16 @@ config XEN_SYSFS
 	help
 	  Xen hypervisor attributes will show up under /sys/hypervisor/.
 
+config XEN_NR_GUEST_DEVICES
+	int "Number of guest devices"
+	range 0 4032 if 64BIT
+	range 0 960
+	default 256 if XEN_BACKEND
+	default 16
+	help
+	  Specify the total number of virtual devices (i.e. both frontend
+	  and backend) that you want the kernel to be able to service.
+
 choice
 	prompt "Xen version compatibility"
 	default XEN_COMPAT_030002_AND_LATER
--- head-2010-04-15.orig/drivers/xen/netback/netback.c	2010-01-04 13:31:26.000000000 +0100
+++ head-2010-04-15/drivers/xen/netback/netback.c	2010-03-25 14:39:26.000000000 +0100
@@ -71,7 +71,7 @@ static DECLARE_TASKLET(net_rx_tasklet, n
 static struct timer_list net_timer;
 static struct timer_list netbk_tx_pending_timer;
 
-#define MAX_PENDING_REQS 256
+#define MAX_PENDING_REQS (1U << CONFIG_XEN_NETDEV_TX_SHIFT)
 
 static struct sk_buff_head rx_queue;
 
@@ -1265,6 +1265,7 @@ static void net_tx_action(unsigned long 
 	net_tx_action_dealloc();
 
 	mop = tx_map_ops;
+	BUILD_BUG_ON(MAX_SKB_FRAGS >= MAX_PENDING_REQS);
 	while (((NR_PENDING_REQS + MAX_SKB_FRAGS) < MAX_PENDING_REQS) &&
 		!list_empty(&net_schedule_list)) {
 		/* Get a netif from the list with work to do. */