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xen/evtchn: improve scalability by using per-user locks
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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>
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David Vrabel authored and Konrad Rzeszutek Wilk committed Aug 9, 2013
1 parent 65a45fa commit 73cc4bb
Showing 1 changed file with 112 additions and 80 deletions.
192 changes: 112 additions & 80 deletions drivers/xen/evtchn.c
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Original file line number Diff line number Diff line change
Expand Up @@ -57,68 +57,95 @@

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))
#define EVTCHN_RING_MASK(_i) ((_i)&(EVTCHN_RING_SIZE-1))
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;
struct fasync_struct *evtchn_async_queue;
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);
Expand All @@ -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;
}
Expand Down Expand Up @@ -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;

Expand All @@ -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;

/*
Expand All @@ -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,
Expand Down Expand Up @@ -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)))
Expand All @@ -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;
}
Expand All @@ -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;
Expand Down Expand Up @@ -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;

Expand All @@ -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);
Expand Down Expand Up @@ -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) {
Expand All @@ -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);
}

Expand Down

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