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vhost: replace vhost_workqueue with per-vhost kthread
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Replace vhost_workqueue with per-vhost kthread.  Other than callback
argument change from struct work_struct * to struct vhost_work *,
there's no visible change to vhost_poll_*() interface.

This conversion is to make each vhost use a dedicated kthread so that
resource control via cgroup can be applied.

Partially based on Sridhar Samudrala's patch.

* Updated to use sub structure vhost_work instead of directly using
  vhost_poll at Michael's suggestion.

* Added flusher wake_up() optimization at Michael's suggestion.

Changes by MST:
* Converted atomics/barrier use to a spinlock.
* Create thread on SET_OWNER
* Fix flushing

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Sridhar Samudrala <samudrala.sridhar@gmail.com>
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Tejun Heo authored and Michael S. Tsirkin committed Jul 28, 2010
1 parent 4cfa580 commit c23f344
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Showing 3 changed files with 164 additions and 73 deletions.
56 changes: 24 additions & 32 deletions drivers/vhost/net.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -302,54 +302,58 @@ static void handle_rx(struct vhost_net *net)
unuse_mm(net->dev.mm);
}

static void handle_tx_kick(struct work_struct *work)
static void handle_tx_kick(struct vhost_work *work)
{
struct vhost_virtqueue *vq;
struct vhost_net *net;
vq = container_of(work, struct vhost_virtqueue, poll.work);
net = container_of(vq->dev, struct vhost_net, dev);
struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
poll.work);
struct vhost_net *net = container_of(vq->dev, struct vhost_net, dev);

handle_tx(net);
}

static void handle_rx_kick(struct work_struct *work)
static void handle_rx_kick(struct vhost_work *work)
{
struct vhost_virtqueue *vq;
struct vhost_net *net;
vq = container_of(work, struct vhost_virtqueue, poll.work);
net = container_of(vq->dev, struct vhost_net, dev);
struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
poll.work);
struct vhost_net *net = container_of(vq->dev, struct vhost_net, dev);

handle_rx(net);
}

static void handle_tx_net(struct work_struct *work)
static void handle_tx_net(struct vhost_work *work)
{
struct vhost_net *net;
net = container_of(work, struct vhost_net, poll[VHOST_NET_VQ_TX].work);
struct vhost_net *net = container_of(work, struct vhost_net,
poll[VHOST_NET_VQ_TX].work);
handle_tx(net);
}

static void handle_rx_net(struct work_struct *work)
static void handle_rx_net(struct vhost_work *work)
{
struct vhost_net *net;
net = container_of(work, struct vhost_net, poll[VHOST_NET_VQ_RX].work);
struct vhost_net *net = container_of(work, struct vhost_net,
poll[VHOST_NET_VQ_RX].work);
handle_rx(net);
}

static int vhost_net_open(struct inode *inode, struct file *f)
{
struct vhost_net *n = kmalloc(sizeof *n, GFP_KERNEL);
struct vhost_dev *dev;
int r;

if (!n)
return -ENOMEM;

dev = &n->dev;
n->vqs[VHOST_NET_VQ_TX].handle_kick = handle_tx_kick;
n->vqs[VHOST_NET_VQ_RX].handle_kick = handle_rx_kick;
r = vhost_dev_init(&n->dev, n->vqs, VHOST_NET_VQ_MAX);
r = vhost_dev_init(dev, n->vqs, VHOST_NET_VQ_MAX);
if (r < 0) {
kfree(n);
return r;
}

vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT);
vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN);
vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, dev);
vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, dev);
n->tx_poll_state = VHOST_NET_POLL_DISABLED;

f->private_data = n;
Expand Down Expand Up @@ -656,25 +660,13 @@ static struct miscdevice vhost_net_misc = {

static int vhost_net_init(void)
{
int r = vhost_init();
if (r)
goto err_init;
r = misc_register(&vhost_net_misc);
if (r)
goto err_reg;
return 0;
err_reg:
vhost_cleanup();
err_init:
return r;

return misc_register(&vhost_net_misc);
}
module_init(vhost_net_init);

static void vhost_net_exit(void)
{
misc_deregister(&vhost_net_misc);
vhost_cleanup();
}
module_exit(vhost_net_exit);

Expand Down
143 changes: 115 additions & 28 deletions drivers/vhost/vhost.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -17,12 +17,12 @@
#include <linux/mm.h>
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/workqueue.h>
#include <linux/rcupdate.h>
#include <linux/poll.h>
#include <linux/file.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/kthread.h>

#include <linux/net.h>
#include <linux/if_packet.h>
Expand All @@ -37,8 +37,6 @@ enum {
VHOST_MEMORY_F_LOG = 0x1,
};

static struct workqueue_struct *vhost_workqueue;

static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
poll_table *pt)
{
Expand All @@ -52,23 +50,31 @@ static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
void *key)
{
struct vhost_poll *poll;
poll = container_of(wait, struct vhost_poll, wait);
struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait);

if (!((unsigned long)key & poll->mask))
return 0;

queue_work(vhost_workqueue, &poll->work);
vhost_poll_queue(poll);
return 0;
}

/* Init poll structure */
void vhost_poll_init(struct vhost_poll *poll, work_func_t func,
unsigned long mask)
void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
unsigned long mask, struct vhost_dev *dev)
{
INIT_WORK(&poll->work, func);
struct vhost_work *work = &poll->work;

init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
init_poll_funcptr(&poll->table, vhost_poll_func);
poll->mask = mask;
poll->dev = dev;

INIT_LIST_HEAD(&work->node);
work->fn = fn;
init_waitqueue_head(&work->done);
work->flushing = 0;
work->queue_seq = work->done_seq = 0;
}

/* Start polling a file. We add ourselves to file's wait queue. The caller must
Expand All @@ -92,12 +98,40 @@ void vhost_poll_stop(struct vhost_poll *poll)
* locks that are also used by the callback. */
void vhost_poll_flush(struct vhost_poll *poll)
{
flush_work(&poll->work);
struct vhost_work *work = &poll->work;
unsigned seq;
int left;
int flushing;

spin_lock_irq(&poll->dev->work_lock);
seq = work->queue_seq;
work->flushing++;
spin_unlock_irq(&poll->dev->work_lock);
wait_event(work->done, ({
spin_lock_irq(&poll->dev->work_lock);
left = seq - work->done_seq <= 0;
spin_unlock_irq(&poll->dev->work_lock);
left;
}));
spin_lock_irq(&poll->dev->work_lock);
flushing = --work->flushing;
spin_unlock_irq(&poll->dev->work_lock);
BUG_ON(flushing < 0);
}

void vhost_poll_queue(struct vhost_poll *poll)
{
queue_work(vhost_workqueue, &poll->work);
struct vhost_dev *dev = poll->dev;
struct vhost_work *work = &poll->work;
unsigned long flags;

spin_lock_irqsave(&dev->work_lock, flags);
if (list_empty(&work->node)) {
list_add_tail(&work->node, &dev->work_list);
work->queue_seq++;
wake_up_process(dev->worker);
}
spin_unlock_irqrestore(&dev->work_lock, flags);
}

static void vhost_vq_reset(struct vhost_dev *dev,
Expand Down Expand Up @@ -125,27 +159,71 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->log_ctx = NULL;
}

static int vhost_worker(void *data)
{
struct vhost_dev *dev = data;
struct vhost_work *work = NULL;
unsigned uninitialized_var(seq);

for (;;) {
/* mb paired w/ kthread_stop */
set_current_state(TASK_INTERRUPTIBLE);

spin_lock_irq(&dev->work_lock);
if (work) {
work->done_seq = seq;
if (work->flushing)
wake_up_all(&work->done);
}

if (kthread_should_stop()) {
spin_unlock_irq(&dev->work_lock);
__set_current_state(TASK_RUNNING);
return 0;
}
if (!list_empty(&dev->work_list)) {
work = list_first_entry(&dev->work_list,
struct vhost_work, node);
list_del_init(&work->node);
seq = work->queue_seq;
} else
work = NULL;
spin_unlock_irq(&dev->work_lock);

if (work) {
__set_current_state(TASK_RUNNING);
work->fn(work);
} else
schedule();

}
}

long vhost_dev_init(struct vhost_dev *dev,
struct vhost_virtqueue *vqs, int nvqs)
{
int i;

dev->vqs = vqs;
dev->nvqs = nvqs;
mutex_init(&dev->mutex);
dev->log_ctx = NULL;
dev->log_file = NULL;
dev->memory = NULL;
dev->mm = NULL;
spin_lock_init(&dev->work_lock);
INIT_LIST_HEAD(&dev->work_list);
dev->worker = NULL;

for (i = 0; i < dev->nvqs; ++i) {
dev->vqs[i].dev = dev;
mutex_init(&dev->vqs[i].mutex);
vhost_vq_reset(dev, dev->vqs + i);
if (dev->vqs[i].handle_kick)
vhost_poll_init(&dev->vqs[i].poll,
dev->vqs[i].handle_kick,
POLLIN);
dev->vqs[i].handle_kick, POLLIN, dev);
}

return 0;
}

Expand All @@ -159,12 +237,31 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
/* Caller should have device mutex */
static long vhost_dev_set_owner(struct vhost_dev *dev)
{
struct task_struct *worker;
int err;
/* Is there an owner already? */
if (dev->mm)
return -EBUSY;
if (dev->mm) {
err = -EBUSY;
goto err_mm;
}
/* No owner, become one */
dev->mm = get_task_mm(current);
worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
if (IS_ERR(worker)) {
err = PTR_ERR(worker);
goto err_worker;
}

dev->worker = worker;
wake_up_process(worker); /* avoid contributing to loadavg */

return 0;
err_worker:
if (dev->mm)
mmput(dev->mm);
dev->mm = NULL;
err_mm:
return err;
}

/* Caller should have device mutex */
Expand Down Expand Up @@ -217,6 +314,9 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
if (dev->mm)
mmput(dev->mm);
dev->mm = NULL;

WARN_ON(!list_empty(&dev->work_list));
kthread_stop(dev->worker);
}

static int log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
Expand Down Expand Up @@ -1115,16 +1215,3 @@ void vhost_disable_notify(struct vhost_virtqueue *vq)
vq_err(vq, "Failed to enable notification at %p: %d\n",
&vq->used->flags, r);
}

int vhost_init(void)
{
vhost_workqueue = create_singlethread_workqueue("vhost");
if (!vhost_workqueue)
return -ENOMEM;
return 0;
}

void vhost_cleanup(void)
{
destroy_workqueue(vhost_workqueue);
}
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