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

Sridhar Samudrala
2010-06-02T21:34:30Z

On 6/2/2010 11:40 AM, Tejun Heo wrote:
> 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.
>

I tested this with 4 VMs running netperf TCP stream tests from guest to
host and i am seeing similar
level of scalability in throughput i saw with the multi-thread workqueue
patch.
11200Mb/s - default (host cpu utilization: 40%)
21600Mb/s - multi-thread (host cpu utilization: 86%)

Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>

Thanks
Sridhar
> 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) \
>