xen/evtchn: improve scalability by using per-user locks

The global array of port users and the port_user_lock limits
scalability of the evtchn device.  Instead of the global array lookup,
use a per-use (per-fd) tree of event channels bound by that user and
protect the tree with a per-user lock.

This is also a prerequiste for extended the number of supported event
channels, by removing the fixed size, per-event channel array.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index b6165e047f48083c5a254dc66a6f4bc3e6e9ddb9..f328f121c92d261aeca13708f6763148298fb7c5 100644 (file)
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -57,6 +57,7 @@
 
 struct per_user_data {
        struct mutex bind_mutex; /* serialize bind/unbind operations */
+       struct rb_root evtchns;
 
        /* Notification ring, accessed via /dev/xen/evtchn. */
 #define EVTCHN_RING_SIZE     (PAGE_SIZE / sizeof(evtchn_port_t))
@@ -64,6 +65,7 @@ struct per_user_data {
        evtchn_port_t *ring;
        unsigned int ring_cons, ring_prod, ring_overflow;
        struct mutex ring_cons_mutex; /* protect against concurrent readers */
+       spinlock_t ring_prod_lock; /* product against concurrent interrupts */
 
        /* Processes wait on this queue when ring is empty. */
        wait_queue_head_t evtchn_wait;
@@ -71,54 +73,79 @@ struct per_user_data {
        const char *name;
 };
 
-/*
- * Who's bound to each port?  This is logically an array of struct
- * per_user_data *, but we encode the current enabled-state in bit 0.
- */
-static unsigned long *port_user;
-static DEFINE_SPINLOCK(port_user_lock); /* protects port_user[] and ring_prod */
+struct user_evtchn {
+       struct rb_node node;
+       struct per_user_data *user;
+       unsigned port;
+       bool enabled;
+};
 
-static inline struct per_user_data *get_port_user(unsigned port)
+static int add_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
 {
-       return (struct per_user_data *)(port_user[port] & ~1);
-}
+       struct rb_node **new = &(u->evtchns.rb_node), *parent = NULL;
 
-static inline void set_port_user(unsigned port, struct per_user_data *u)
-{
-       port_user[port] = (unsigned long)u;
+       while (*new) {
+               struct user_evtchn *this;
+
+               this = container_of(*new, struct user_evtchn, node);
+
+               parent = *new;
+               if (this->port < evtchn->port)
+                       new = &((*new)->rb_left);
+               else if (this->port > evtchn->port)
+                       new = &((*new)->rb_right);
+               else
+                       return -EEXIST;
+       }
+
+       /* Add new node and rebalance tree. */
+       rb_link_node(&evtchn->node, parent, new);
+       rb_insert_color(&evtchn->node, &u->evtchns);
+
+       return 0;
 }
 
-static inline bool get_port_enabled(unsigned port)
+static void del_evtchn(struct per_user_data *u, struct user_evtchn *evtchn)
 {
-       return port_user[port] & 1;
+       rb_erase(&evtchn->node, &u->evtchns);
+       kfree(evtchn);
 }
 
-static inline void set_port_enabled(unsigned port, bool enabled)
+static struct user_evtchn *find_evtchn(struct per_user_data *u, unsigned port)
 {
-       if (enabled)
-               port_user[port] |= 1;
-       else
-               port_user[port] &= ~1;
+       struct rb_node *node = u->evtchns.rb_node;
+
+       while (node) {
+               struct user_evtchn *evtchn;
+
+               evtchn = container_of(node, struct user_evtchn, node);
+
+               if (evtchn->port < port)
+                       node = node->rb_left;
+               else if (evtchn->port > port)
+                       node = node->rb_right;
+               else
+                       return evtchn;
+       }
+       return NULL;
 }
 
 static irqreturn_t evtchn_interrupt(int irq, void *data)
 {
-       unsigned int port = (unsigned long)data;
-       struct per_user_data *u;
-
-       spin_lock(&port_user_lock);
-
-       u = get_port_user(port);
+       struct user_evtchn *evtchn = data;
+       struct per_user_data *u = evtchn->user;
 
-       WARN(!get_port_enabled(port),
+       WARN(!evtchn->enabled,
             "Interrupt for port %d, but apparently not enabled; per-user %p\n",
-            port, u);
+            evtchn->port, u);
 
        disable_irq_nosync(irq);
-       set_port_enabled(port, false);
+       evtchn->enabled = false;
+
+       spin_lock(&u->ring_prod_lock);
 
        if ((u->ring_prod - u->ring_cons) < EVTCHN_RING_SIZE) {
-               u->ring[EVTCHN_RING_MASK(u->ring_prod)] = port;
+               u->ring[EVTCHN_RING_MASK(u->ring_prod)] = evtchn->port;
                wmb(); /* Ensure ring contents visible */
                if (u->ring_cons == u->ring_prod++) {
                        wake_up_interruptible(&u->evtchn_wait);
@@ -128,7 +155,7 @@ static irqreturn_t evtchn_interrupt(int irq, void *data)
        } else
                u->ring_overflow = 1;
 
-       spin_unlock(&port_user_lock);
+       spin_unlock(&u->ring_prod_lock);
 
        return IRQ_HANDLED;
 }
@@ -229,20 +256,20 @@ static ssize_t evtchn_write(struct file *file, const char __user *buf,
        if (copy_from_user(kbuf, buf, count) != 0)
                goto out;
 
-       spin_lock_irq(&port_user_lock);
+       mutex_lock(&u->bind_mutex);
 
        for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
                unsigned port = kbuf[i];
+               struct user_evtchn *evtchn;
 
-               if (port < NR_EVENT_CHANNELS &&
-                   get_port_user(port) == u &&
-                   !get_port_enabled(port)) {
-                       set_port_enabled(port, true);
+               evtchn = find_evtchn(u, port);
+               if (evtchn && !evtchn->enabled) {
+                       evtchn->enabled = true;
                        enable_irq(irq_from_evtchn(port));
                }
        }
 
-       spin_unlock_irq(&port_user_lock);
+       mutex_unlock(&u->bind_mutex);
 
        rc = count;
 
@@ -253,6 +280,8 @@ static ssize_t evtchn_write(struct file *file, const char __user *buf,
 
 static int evtchn_bind_to_user(struct per_user_data *u, int port)
 {
+       struct user_evtchn *evtchn;
+       struct evtchn_close close;
        int rc = 0;
 
        /*
@@ -263,35 +292,47 @@ static int evtchn_bind_to_user(struct per_user_data *u, int port)
         * interrupt handler yet, and our caller has already
         * serialized bind operations.)
         */
-       BUG_ON(get_port_user(port) != NULL);
-       set_port_user(port, u);
-       set_port_enabled(port, true); /* start enabled */
+
+       evtchn = kzalloc(sizeof(*evtchn), GFP_KERNEL);
+       if (!evtchn)
+               return -ENOMEM;
+
+       evtchn->user = u;
+       evtchn->port = port;
+       evtchn->enabled = true; /* start enabled */
+
+       rc = add_evtchn(u, evtchn);
+       if (rc < 0)
+               goto err;
 
        rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, IRQF_DISABLED,
-                                      u->name, (void *)(unsigned long)port);
-       if (rc >= 0)
-               rc = evtchn_make_refcounted(port);
-       else {
-               /* bind failed, should close the port now */
-               struct evtchn_close close;
-               close.port = port;
-               if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
-                       BUG();
-               set_port_user(port, NULL);
-       }
+                                      u->name, evtchn);
+       if (rc < 0)
+               goto err;
 
+       rc = evtchn_make_refcounted(port);
+       return rc;
+
+err:
+       /* bind failed, should close the port now */
+       close.port = port;
+       if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
+               BUG();
+       del_evtchn(u, evtchn);
+       kfree(evtchn);
        return rc;
 }
 
-static void evtchn_unbind_from_user(struct per_user_data *u, int port)
+static void evtchn_unbind_from_user(struct per_user_data *u,
+                                   struct user_evtchn *evtchn)
 {
-       int irq = irq_from_evtchn(port);
+       int irq = irq_from_evtchn(evtchn->port);
 
        BUG_ON(irq < 0);
 
-       unbind_from_irqhandler(irq, (void *)(unsigned long)port);
+       unbind_from_irqhandler(irq, evtchn);
 
-       set_port_user(port, NULL);
+       del_evtchn(u, evtchn);
 }
 
 static long evtchn_ioctl(struct file *file,
@@ -370,6 +411,7 @@ static long evtchn_ioctl(struct file *file,
 
        case IOCTL_EVTCHN_UNBIND: {
                struct ioctl_evtchn_unbind unbind;
+               struct user_evtchn *evtchn;
 
                rc = -EFAULT;
                if (copy_from_user(&unbind, uarg, sizeof(unbind)))
@@ -380,29 +422,27 @@ static long evtchn_ioctl(struct file *file,
                        break;
 
                rc = -ENOTCONN;
-               if (get_port_user(unbind.port) != u)
+               evtchn = find_evtchn(u, unbind.port);
+               if (!evtchn)
                        break;
 
                disable_irq(irq_from_evtchn(unbind.port));
-
-               evtchn_unbind_from_user(u, unbind.port);
-
+               evtchn_unbind_from_user(u, evtchn);
                rc = 0;
                break;
        }
 
        case IOCTL_EVTCHN_NOTIFY: {
                struct ioctl_evtchn_notify notify;
+               struct user_evtchn *evtchn;
 
                rc = -EFAULT;
                if (copy_from_user(&notify, uarg, sizeof(notify)))
                        break;
 
-               if (notify.port >= NR_EVENT_CHANNELS) {
-                       rc = -EINVAL;
-               } else if (get_port_user(notify.port) != u) {
-                       rc = -ENOTCONN;
-               } else {
+               rc = -ENOTCONN;
+               evtchn = find_evtchn(u, notify.port);
+               if (evtchn) {
                        notify_remote_via_evtchn(notify.port);
                        rc = 0;
                }
@@ -412,9 +452,9 @@ static long evtchn_ioctl(struct file *file,
        case IOCTL_EVTCHN_RESET: {
                /* Initialise the ring to empty. Clear errors. */
                mutex_lock(&u->ring_cons_mutex);
-               spin_lock_irq(&port_user_lock);
+               spin_lock_irq(&u->ring_prod_lock);
                u->ring_cons = u->ring_prod = u->ring_overflow = 0;
-               spin_unlock_irq(&port_user_lock);
+               spin_unlock_irq(&u->ring_prod_lock);
                mutex_unlock(&u->ring_cons_mutex);
                rc = 0;
                break;
@@ -473,6 +513,7 @@ static int evtchn_open(struct inode *inode, struct file *filp)
 
        mutex_init(&u->bind_mutex);
        mutex_init(&u->ring_cons_mutex);
+       spin_lock_init(&u->ring_prod_lock);
 
        filp->private_data = u;
 
@@ -481,15 +522,15 @@ static int evtchn_open(struct inode *inode, struct file *filp)
 
 static int evtchn_release(struct inode *inode, struct file *filp)
 {
-       int i;
        struct per_user_data *u = filp->private_data;
+       struct rb_node *node;
 
-       for (i = 0; i < NR_EVENT_CHANNELS; i++) {
-               if (get_port_user(i) != u)
-                       continue;
+       while ((node = u->evtchns.rb_node)) {
+               struct user_evtchn *evtchn;
 
-               disable_irq(irq_from_evtchn(i));
-               evtchn_unbind_from_user(get_port_user(i), i);
+               evtchn = rb_entry(node, struct user_evtchn, node);
+               disable_irq(irq_from_evtchn(evtchn->port));
+               evtchn_unbind_from_user(u, evtchn);
        }
 
        free_page((unsigned long)u->ring);
@@ -523,12 +564,6 @@ static int __init evtchn_init(void)
        if (!xen_domain())
                return -ENODEV;
 
-       port_user = kcalloc(NR_EVENT_CHANNELS, sizeof(*port_user), GFP_KERNEL);
-       if (port_user == NULL)
-               return -ENOMEM;
-
-       spin_lock_init(&port_user_lock);
-
        /* Create '/dev/xen/evtchn'. */
        err = misc_register(&evtchn_miscdev);
        if (err != 0) {
@@ -543,9 +578,6 @@ static int __init evtchn_init(void)
 
 static void __exit evtchn_cleanup(void)
 {
-       kfree(port_user);
-       port_user = NULL;
-
        misc_deregister(&evtchn_miscdev);
 }