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Subject[PATCH UPDATED 1/3] vhost: replace vhost_workqueue with per-vhost kthread
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.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Sridhar Samudrala <samudrala.sridhar@gmail.com>
---
Okay, just tested it. dev->work_lock had to be updated to use irq
operations but other than that it worked just fine. Copied a large
file using scp and it seems to perform pretty well although I don't
have any reference of comparison. So, here's the updated version with
the sign off.
Thanks.

drivers/vhost/net.c | 56 ++++++++++---------------
drivers/vhost/vhost.c | 111 ++++++++++++++++++++++++++++++++++++++------------
drivers/vhost/vhost.h | 38 +++++++++++------
3 files changed, 134 insertions(+), 71 deletions(-)
Index: work/drivers/vhost/net.c
===================================================================
--- work.orig/drivers/vhost/net.c
+++ work/drivers/vhost/net.c
@@ -294,54 +294,58 @@ static void handle_rx(struct vhost_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;
@@ -644,25 +648,13 @@ 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);

Index: work/drivers/vhost/vhost.c
===================================================================
--- work.orig/drivers/vhost/vhost.c
+++ work/drivers/vhost/vhost.c
@@ -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>
@@ -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)
{
@@ -52,23 +50,31 @@ static void vhost_poll_func(struct file
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);
+ atomic_set(&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
@@ -92,12 +98,29 @@ void vhost_poll_stop(struct vhost_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;
+ int seq = work->queue_seq;
+
+ atomic_inc(&work->flushing);
+ smp_mb__after_atomic_inc(); /* mb flush-b0 paired with worker-b1 */
+ wait_event(work->done, seq - work->done_seq <= 0);
+ atomic_dec(&work->flushing);
+ smp_mb__after_atomic_dec(); /* rmb flush-b1 paired with worker-b0 */
}

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,
@@ -125,10 +148,52 @@ static void vhost_vq_reset(struct vhost_
vq->log_ctx = NULL;
}

+static int vhost_worker(void *data)
+{
+ struct vhost_dev *dev = data;
+ struct vhost_work *work;
+
+repeat:
+ set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
+
+ if (kthread_should_stop()) {
+ __set_current_state(TASK_RUNNING);
+ return 0;
+ }
+
+ work = NULL;
+ spin_lock_irq(&dev->work_lock);
+ if (!list_empty(&dev->work_list)) {
+ work = list_first_entry(&dev->work_list,
+ struct vhost_work, node);
+ list_del_init(&work->node);
+ }
+ spin_unlock_irq(&dev->work_lock);
+
+ if (work) {
+ __set_current_state(TASK_RUNNING);
+ work->fn(work);
+ smp_wmb(); /* wmb worker-b0 paired with flush-b1 */
+ work->done_seq = work->queue_seq;
+ smp_mb(); /* mb worker-b1 paired with flush-b0 */
+ if (atomic_read(&work->flushing))
+ wake_up_all(&work->done);
+ } else
+ schedule();
+
+ goto repeat;
+}
+
long vhost_dev_init(struct vhost_dev *dev,
struct vhost_virtqueue *vqs, int nvqs)
{
+ struct task_struct *worker;
int i;
+
+ worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
+ if (IS_ERR(worker))
+ return PTR_ERR(worker);
+
dev->vqs = vqs;
dev->nvqs = nvqs;
mutex_init(&dev->mutex);
@@ -136,6 +201,9 @@ long vhost_dev_init(struct vhost_dev *de
dev->log_file = NULL;
dev->memory = NULL;
dev->mm = NULL;
+ spin_lock_init(&dev->work_lock);
+ INIT_LIST_HEAD(&dev->work_list);
+ dev->worker = worker;

for (i = 0; i < dev->nvqs; ++i) {
dev->vqs[i].dev = dev;
@@ -143,9 +211,10 @@ long vhost_dev_init(struct vhost_dev *de
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);
}
+
+ wake_up_process(worker); /* avoid contributing to loadavg */
return 0;
}

@@ -217,6 +286,9 @@ void vhost_dev_cleanup(struct vhost_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)
@@ -1113,16 +1185,3 @@ void vhost_disable_notify(struct vhost_v
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);
-}
Index: work/drivers/vhost/vhost.h
===================================================================
--- work.orig/drivers/vhost/vhost.h
+++ work/drivers/vhost/vhost.h
@@ -5,13 +5,13 @@
#include <linux/vhost.h>
#include <linux/mm.h>
#include <linux/mutex.h>
-#include <linux/workqueue.h>
#include <linux/poll.h>
#include <linux/file.h>
#include <linux/skbuff.h>
#include <linux/uio.h>
#include <linux/virtio_config.h>
#include <linux/virtio_ring.h>
+#include <asm/atomic.h>

struct vhost_device;

@@ -20,19 +20,31 @@ enum {
VHOST_NET_MAX_SG = MAX_SKB_FRAGS + 2,
};

+struct vhost_work;
+typedef void (*vhost_work_fn_t)(struct vhost_work *work);
+
+struct vhost_work {
+ struct list_head node;
+ vhost_work_fn_t fn;
+ wait_queue_head_t done;
+ atomic_t flushing;
+ int queue_seq;
+ int done_seq;
+};
+
/* Poll a file (eventfd or socket) */
/* Note: there's nothing vhost specific about this structure. */
struct vhost_poll {
poll_table table;
wait_queue_head_t *wqh;
wait_queue_t wait;
- /* struct which will handle all actual work. */
- struct work_struct work;
+ struct vhost_work work;
unsigned long mask;
+ struct vhost_dev *dev;
};

-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);
void vhost_poll_start(struct vhost_poll *poll, struct file *file);
void vhost_poll_stop(struct vhost_poll *poll);
void vhost_poll_flush(struct vhost_poll *poll);
@@ -63,7 +75,7 @@ struct vhost_virtqueue {
struct vhost_poll poll;

/* The routine to call when the Guest pings us, or timeout. */
- work_func_t handle_kick;
+ vhost_work_fn_t handle_kick;

/* Last available index we saw. */
u16 last_avail_idx;
@@ -86,11 +98,11 @@ struct vhost_virtqueue {
struct iovec hdr[VHOST_NET_MAX_SG];
size_t hdr_size;
/* We use a kind of RCU to access private pointer.
- * All readers access it from workqueue, which makes it possible to
- * flush the workqueue instead of synchronize_rcu. Therefore readers do
+ * All readers access it from worker, which makes it possible to
+ * flush the vhost_work instead of synchronize_rcu. Therefore readers do
* not need to call rcu_read_lock/rcu_read_unlock: the beginning of
- * work item execution acts instead of rcu_read_lock() and the end of
- * work item execution acts instead of rcu_read_lock().
+ * vhost_work execution acts instead of rcu_read_lock() and the end of
+ * vhost_work execution acts instead of rcu_read_lock().
* Writers use virtqueue mutex. */
void *private_data;
/* Log write descriptors */
@@ -110,6 +122,9 @@ struct vhost_dev {
int nvqs;
struct file *log_file;
struct eventfd_ctx *log_ctx;
+ spinlock_t work_lock;
+ struct list_head work_list;
+ struct task_struct *worker;
};

long vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue *vqs, int nvqs);
@@ -136,9 +151,6 @@ bool vhost_enable_notify(struct vhost_vi
int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
unsigned int log_num, u64 len);

-int vhost_init(void);
-void vhost_cleanup(void);
-
#define vq_err(vq, fmt, ...) do { \
pr_debug(pr_fmt(fmt), ##__VA_ARGS__); \
if ((vq)->error_ctx) \

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