[RFC PATCH V3 10/16] netback: rework of per-cpu scratch space.

[Wei Liu <wei.liu2@citrix.com>]

If we allocate large arrays in per-cpu section, multi-page ring
feature is likely to blow up the per-cpu section. So avoid allocating
large arrays, instead we only store pointers to scratch spaces in
per-cpu section.

CPU hotplug event is also taken care of.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
 drivers/net/xen-netback/netback.c |  140 +++++++++++++++++++++++++++----------
 1 files changed, 104 insertions(+), 36 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index a8d58a9..2ac9b84 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -39,6 +39,7 @@
 #include <linux/kthread.h>
 #include <linux/if_vlan.h>
 #include <linux/udp.h>
+#include <linux/cpu.h>
 
 #include <net/tcp.h>
 
@@ -49,15 +50,15 @@
 #include <asm/xen/page.h>
 
 
-struct gnttab_copy *tx_copy_ops;
+DEFINE_PER_CPU(struct gnttab_copy *, tx_copy_ops);
 
 /*
  * Given MAX_BUFFER_OFFSET of 4096 the worst case is that each
  * head/fragment page uses 2 copy operations because it
  * straddles two buffers in the frontend.
  */
-struct gnttab_copy *grant_copy_op;
-struct xenvif_rx_meta *meta;
+DEFINE_PER_CPU(struct gnttab_copy *, grant_copy_op);
+DEFINE_PER_CPU(struct xenvif_rx_meta *, meta);
 
 static void xenvif_idx_release(struct xenvif *vif, u16 pending_idx);
 static void make_tx_response(struct xenvif *vif,
@@ -481,8 +482,8 @@ void xenvif_rx_action(struct xenvif *vif)
 	struct skb_cb_overlay *sco;
 	int need_to_notify = 0;
 
-	struct gnttab_copy *gco = get_cpu_ptr(grant_copy_op);
-	struct xenvif_rx_meta *m = get_cpu_ptr(meta);
+	struct gnttab_copy *gco = get_cpu_var(grant_copy_op);
+	struct xenvif_rx_meta *m = get_cpu_var(meta);
 
 	struct netrx_pending_operations npo = {
 		.copy  = gco,
@@ -512,8 +513,8 @@ void xenvif_rx_action(struct xenvif *vif)
 	BUG_ON(npo.meta_prod > MAX_PENDING_REQS);
 
 	if (!npo.copy_prod) {
-		put_cpu_ptr(gco);
-		put_cpu_ptr(m);
+		put_cpu_var(grant_copy_op);
+		put_cpu_var(meta);
 		return;
 	}
 
@@ -599,8 +600,8 @@ void xenvif_rx_action(struct xenvif *vif)
 	if (!skb_queue_empty(&vif->rx_queue))
 		xenvif_kick_thread(vif);
 
-	put_cpu_ptr(gco);
-	put_cpu_ptr(m);
+	put_cpu_var(grant_copy_op);
+	put_cpu_var(meta);
 }
 
 void xenvif_queue_tx_skb(struct xenvif *vif, struct sk_buff *skb)
@@ -1287,12 +1288,12 @@ int xenvif_tx_action(struct xenvif *vif, int budget)
 	if (unlikely(!tx_work_todo(vif)))
 		return 0;
 
-	tco = get_cpu_ptr(tx_copy_ops);
+	tco = get_cpu_var(tx_copy_ops);
 
 	nr_gops = xenvif_tx_build_gops(vif, tco);
 
 	if (nr_gops == 0) {
-		put_cpu_ptr(tco);
+		put_cpu_var(tx_copy_ops);
 		return 0;
 	}
 
@@ -1301,7 +1302,7 @@ int xenvif_tx_action(struct xenvif *vif, int budget)
 
 	work_done = xenvif_tx_submit(vif, tco, budget);
 
-	put_cpu_ptr(tco);
+	put_cpu_var(tx_copy_ops);
 
 	return work_done;
 }
@@ -1452,31 +1453,97 @@ int xenvif_kthread(void *data)
 	return 0;
 }
 
+static int __create_percpu_scratch_space(unsigned int cpu)
+{
+	per_cpu(tx_copy_ops, cpu) =
+		vzalloc(sizeof(struct gnttab_copy) * MAX_PENDING_REQS);
+
+	per_cpu(grant_copy_op, cpu) =
+		vzalloc(sizeof(struct gnttab_copy)
+			* 2 * XEN_NETIF_RX_RING_SIZE);
+
+	per_cpu(meta, cpu) = vzalloc(sizeof(struct xenvif_rx_meta)
+				     * 2 * XEN_NETIF_RX_RING_SIZE);
+
+	if (!per_cpu(tx_copy_ops, cpu) ||
+	    !per_cpu(grant_copy_op, cpu) ||
+	    !per_cpu(meta, cpu))
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void __free_percpu_scratch_space(unsigned int cpu)
+{
+	/* freeing NULL pointer is legit */
+	vfree(per_cpu(tx_copy_ops, cpu));
+	vfree(per_cpu(grant_copy_op, cpu));
+	vfree(per_cpu(meta, cpu));
+}
+
+static int __netback_percpu_callback(struct notifier_block *nfb,
+				     unsigned long action, void *hcpu)
+{
+	unsigned int cpu = (unsigned long)hcpu;
+	int rc = NOTIFY_DONE;
+
+	switch (action) {
+	case CPU_ONLINE:
+	case CPU_ONLINE_FROZEN:
+		printk(KERN_INFO
+		       "netback: CPU %x online, creating scratch space\n", cpu);
+		rc = __create_percpu_scratch_space(cpu);
+		if (rc) {
+			printk(KERN_ALERT
+			       "netback: failed to create scratch space for CPU"
+			       " %x\n", cpu);
+			/* FIXME: nothing more we can do here, we will
+			 * print out warning message when thread or
+			 * NAPI runs on this cpu. Also stop getting
+			 * called in the future.
+			 */
+			__free_percpu_scratch_space(cpu);
+			rc = NOTIFY_BAD;
+		} else {
+			rc = NOTIFY_OK;
+		}
+		break;
+	case CPU_DEAD:
+	case CPU_DEAD_FROZEN:
+		printk("netback: CPU %x offline, destroying scratch space\n",
+		       cpu);
+		__free_percpu_scratch_space(cpu);
+		rc = NOTIFY_OK;
+		break;
+	default:
+		break;
+	}
+
+	return rc;
+}
+
+static struct notifier_block netback_notifier_block = {
+	.notifier_call = __netback_percpu_callback,
+};
 
 static int __init netback_init(void)
 {
 	int rc = -ENOMEM;
+	int cpu;
 
 	if (!xen_domain())
 		return -ENODEV;
 
-	tx_copy_ops = __alloc_percpu(sizeof(struct gnttab_copy)
-				     * MAX_PENDING_REQS,
-				     __alignof__(struct gnttab_copy));
-	if (!tx_copy_ops)
-		goto failed_init;
+	/* Don't need to disable preempt here, since nobody else will
+	 * touch these percpu areas during start up. */
+	for_each_online_cpu(cpu) {
+		rc = __create_percpu_scratch_space(cpu);
 
-	grant_copy_op = __alloc_percpu(sizeof(struct gnttab_copy)
-				       * 2 * XEN_NETIF_RX_RING_SIZE,
-				       __alignof__(struct gnttab_copy));
-	if (!grant_copy_op)
-		goto failed_init_gco;
+		if (rc)
+			goto failed_init;
+	}
 
-	meta = __alloc_percpu(sizeof(struct xenvif_rx_meta)
-			      * 2 * XEN_NETIF_RX_RING_SIZE,
-			      __alignof__(struct xenvif_rx_meta));
-	if (!meta)
-		goto failed_init_meta;
+	register_hotcpu_notifier(&netback_notifier_block);
 
 	rc = page_pool_init();
 	if (rc)
@@ -1491,25 +1558,26 @@ static int __init netback_init(void)
 failed_init_xenbus:
 	page_pool_destroy();
 failed_init_pool:
-	free_percpu(meta);
-failed_init_meta:
-	free_percpu(grant_copy_op);
-failed_init_gco:
-	free_percpu(tx_copy_ops);
+	for_each_online_cpu(cpu)
+		__free_percpu_scratch_space(cpu);
 failed_init:
 	return rc;
-
 }
 
 module_init(netback_init);
 
 static void __exit netback_exit(void)
 {
+	int cpu;
+
 	xenvif_xenbus_exit();
 	page_pool_destroy();
-	free_percpu(meta);
-	free_percpu(grant_copy_op);
-	free_percpu(tx_copy_ops);
+
+	unregister_hotcpu_notifier(&netback_notifier_block);
+
+	/* Since we're here, nobody else will touch per-cpu area. */
+	for_each_online_cpu(cpu)
+		__free_percpu_scratch_space(cpu);
 }
 module_exit(netback_exit);
 
-- 
1.7.2.5