Re: [RFC PATCH 1/4] vhost: Introduce a universal thread to serve all users
From: Michael S. Tsirkin
Date: Mon Aug 10 2015 - 05:28:10 EST
On Mon, Jul 13, 2015 at 12:07:32AM -0400, Bandan Das wrote:
> vhost threads are per-device, but in most cases a single thread
> is enough. This change creates a single thread that is used to
> serve all guests.
>
> However, this complicates cgroups associations. The current policy
> is to attach the per-device thread to all cgroups of the parent process
> that the device is associated it. This is no longer possible if we
> have a single thread. So, we end up moving the thread around to
> cgroups of whichever device that needs servicing. This is a very
> inefficient protocol but seems to be the only way to integrate
> cgroups support.
>
> Signed-off-by: Razya Ladelsky <razya@xxxxxxxxxx>
> Signed-off-by: Bandan Das <bsd@xxxxxxxxxx>
BTW, how does this interact with virtio net MQ?
It would seem that MQ gains from more parallelism and
CPU locality.
> ---
> drivers/vhost/scsi.c | 15 +++--
> drivers/vhost/vhost.c | 150 ++++++++++++++++++++++++--------------------------
> drivers/vhost/vhost.h | 19 +++++--
> 3 files changed, 97 insertions(+), 87 deletions(-)
>
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index ea32b38..6c42936 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -535,7 +535,7 @@ static void vhost_scsi_complete_cmd(struct vhost_scsi_cmd *cmd)
>
> llist_add(&cmd->tvc_completion_list, &vs->vs_completion_list);
>
> - vhost_work_queue(&vs->dev, &vs->vs_completion_work);
> + vhost_work_queue(vs->dev.worker, &vs->vs_completion_work);
> }
>
> static int vhost_scsi_queue_data_in(struct se_cmd *se_cmd)
> @@ -1282,7 +1282,7 @@ vhost_scsi_send_evt(struct vhost_scsi *vs,
> }
>
> llist_add(&evt->list, &vs->vs_event_list);
> - vhost_work_queue(&vs->dev, &vs->vs_event_work);
> + vhost_work_queue(vs->dev.worker, &vs->vs_event_work);
> }
>
> static void vhost_scsi_evt_handle_kick(struct vhost_work *work)
> @@ -1335,8 +1335,8 @@ static void vhost_scsi_flush(struct vhost_scsi *vs)
> /* Flush both the vhost poll and vhost work */
> for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
> vhost_scsi_flush_vq(vs, i);
> - vhost_work_flush(&vs->dev, &vs->vs_completion_work);
> - vhost_work_flush(&vs->dev, &vs->vs_event_work);
> + vhost_work_flush(vs->dev.worker, &vs->vs_completion_work);
> + vhost_work_flush(vs->dev.worker, &vs->vs_event_work);
>
> /* Wait for all reqs issued before the flush to be finished */
> for (i = 0; i < VHOST_SCSI_MAX_VQ; i++)
> @@ -1584,8 +1584,11 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
> if (!vqs)
> goto err_vqs;
>
> - vhost_work_init(&vs->vs_completion_work, vhost_scsi_complete_cmd_work);
> - vhost_work_init(&vs->vs_event_work, vhost_scsi_evt_work);
> + vhost_work_init(&vs->dev, &vs->vs_completion_work,
> + vhost_scsi_complete_cmd_work);
> +
> + vhost_work_init(&vs->dev, &vs->vs_event_work,
> + vhost_scsi_evt_work);
>
> vs->vs_events_nr = 0;
> vs->vs_events_missed = false;
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 2ee2826..951c96b 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -11,6 +11,8 @@
> * Generic code for virtio server in host kernel.
> */
>
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> #include <linux/eventfd.h>
> #include <linux/vhost.h>
> #include <linux/uio.h>
> @@ -28,6 +30,9 @@
>
> #include "vhost.h"
>
> +/* Just one worker thread to service all devices */
> +static struct vhost_worker *worker;
> +
> enum {
> VHOST_MEMORY_MAX_NREGIONS = 64,
> VHOST_MEMORY_F_LOG = 0x1,
> @@ -58,13 +63,15 @@ static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
> return 0;
> }
>
> -void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
> +void vhost_work_init(struct vhost_dev *dev,
> + struct vhost_work *work, vhost_work_fn_t fn)
> {
> INIT_LIST_HEAD(&work->node);
> work->fn = fn;
> init_waitqueue_head(&work->done);
> work->flushing = 0;
> work->queue_seq = work->done_seq = 0;
> + work->dev = dev;
> }
> EXPORT_SYMBOL_GPL(vhost_work_init);
>
> @@ -78,7 +85,7 @@ void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
> poll->dev = dev;
> poll->wqh = NULL;
>
> - vhost_work_init(&poll->work, fn);
> + vhost_work_init(dev, &poll->work, fn);
> }
> EXPORT_SYMBOL_GPL(vhost_poll_init);
>
> @@ -116,30 +123,30 @@ void vhost_poll_stop(struct vhost_poll *poll)
> }
> EXPORT_SYMBOL_GPL(vhost_poll_stop);
>
> -static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,
> - unsigned seq)
> +static bool vhost_work_seq_done(struct vhost_worker *worker,
> + struct vhost_work *work, unsigned seq)
> {
> int left;
>
> - spin_lock_irq(&dev->work_lock);
> + spin_lock_irq(&worker->work_lock);
> left = seq - work->done_seq;
> - spin_unlock_irq(&dev->work_lock);
> + spin_unlock_irq(&worker->work_lock);
> return left <= 0;
> }
>
> -void vhost_work_flush(struct vhost_dev *dev, struct vhost_work *work)
> +void vhost_work_flush(struct vhost_worker *worker, struct vhost_work *work)
> {
> unsigned seq;
> int flushing;
>
> - spin_lock_irq(&dev->work_lock);
> + spin_lock_irq(&worker->work_lock);
> seq = work->queue_seq;
> work->flushing++;
> - spin_unlock_irq(&dev->work_lock);
> - wait_event(work->done, vhost_work_seq_done(dev, work, seq));
> - spin_lock_irq(&dev->work_lock);
> + spin_unlock_irq(&worker->work_lock);
> + wait_event(work->done, vhost_work_seq_done(worker, work, seq));
> + spin_lock_irq(&worker->work_lock);
> flushing = --work->flushing;
> - spin_unlock_irq(&dev->work_lock);
> + spin_unlock_irq(&worker->work_lock);
> BUG_ON(flushing < 0);
> }
> EXPORT_SYMBOL_GPL(vhost_work_flush);
> @@ -148,29 +155,30 @@ EXPORT_SYMBOL_GPL(vhost_work_flush);
> * locks that are also used by the callback. */
> void vhost_poll_flush(struct vhost_poll *poll)
> {
> - vhost_work_flush(poll->dev, &poll->work);
> + vhost_work_flush(poll->dev->worker, &poll->work);
> }
> EXPORT_SYMBOL_GPL(vhost_poll_flush);
>
> -void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
> +void vhost_work_queue(struct vhost_worker *worker,
> + struct vhost_work *work)
> {
> unsigned long flags;
>
> - spin_lock_irqsave(&dev->work_lock, flags);
> + spin_lock_irqsave(&worker->work_lock, flags);
> if (list_empty(&work->node)) {
> - list_add_tail(&work->node, &dev->work_list);
> + list_add_tail(&work->node, &worker->work_list);
> work->queue_seq++;
> - spin_unlock_irqrestore(&dev->work_lock, flags);
> - wake_up_process(dev->worker);
> + spin_unlock_irqrestore(&worker->work_lock, flags);
> + wake_up_process(worker->thread);
> } else {
> - spin_unlock_irqrestore(&dev->work_lock, flags);
> + spin_unlock_irqrestore(&worker->work_lock, flags);
> }
> }
> EXPORT_SYMBOL_GPL(vhost_work_queue);
>
> void vhost_poll_queue(struct vhost_poll *poll)
> {
> - vhost_work_queue(poll->dev, &poll->work);
> + vhost_work_queue(poll->dev->worker, &poll->work);
> }
> EXPORT_SYMBOL_GPL(vhost_poll_queue);
>
> @@ -203,19 +211,18 @@ static void vhost_vq_reset(struct vhost_dev *dev,
>
> static int vhost_worker(void *data)
> {
> - struct vhost_dev *dev = data;
> + struct vhost_worker *worker = data;
> struct vhost_work *work = NULL;
> unsigned uninitialized_var(seq);
> mm_segment_t oldfs = get_fs();
>
> set_fs(USER_DS);
> - use_mm(dev->mm);
>
> for (;;) {
> /* mb paired w/ kthread_stop */
> set_current_state(TASK_INTERRUPTIBLE);
>
> - spin_lock_irq(&dev->work_lock);
> + spin_lock_irq(&worker->work_lock);
> if (work) {
> work->done_seq = seq;
> if (work->flushing)
> @@ -223,21 +230,35 @@ static int vhost_worker(void *data)
> }
>
> if (kthread_should_stop()) {
> - spin_unlock_irq(&dev->work_lock);
> + spin_unlock_irq(&worker->work_lock);
> __set_current_state(TASK_RUNNING);
> break;
> }
> - if (!list_empty(&dev->work_list)) {
> - work = list_first_entry(&dev->work_list,
> + if (!list_empty(&worker->work_list)) {
> + work = list_first_entry(&worker->work_list,
> struct vhost_work, node);
> list_del_init(&work->node);
> seq = work->queue_seq;
> } else
> work = NULL;
> - spin_unlock_irq(&dev->work_lock);
> + spin_unlock_irq(&worker->work_lock);
>
> if (work) {
> + struct vhost_dev *dev = work->dev;
> +
> __set_current_state(TASK_RUNNING);
> +
> + if (current->mm != dev->mm) {
> + unuse_mm(current->mm);
> + use_mm(dev->mm);
> + }
> +
> + /* TODO: Consider a more elegant solution */
> + if (worker->owner != dev->owner) {
> + /* Should check for return value */
> + cgroup_attach_task_all(dev->owner, current);
> + worker->owner = dev->owner;
> + }
> work->fn(work);
> if (need_resched())
> schedule();
> @@ -245,7 +266,6 @@ static int vhost_worker(void *data)
> schedule();
>
> }
> - unuse_mm(dev->mm);
> set_fs(oldfs);
> return 0;
> }
> @@ -304,9 +324,8 @@ void vhost_dev_init(struct vhost_dev *dev,
> 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;
> + dev->worker = worker;
> + dev->owner = current;
>
> for (i = 0; i < dev->nvqs; ++i) {
> vq = dev->vqs[i];
> @@ -331,31 +350,6 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
> }
> EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
>
> -struct vhost_attach_cgroups_struct {
> - struct vhost_work work;
> - struct task_struct *owner;
> - int ret;
> -};
> -
> -static void vhost_attach_cgroups_work(struct vhost_work *work)
> -{
> - struct vhost_attach_cgroups_struct *s;
> -
> - s = container_of(work, struct vhost_attach_cgroups_struct, work);
> - s->ret = cgroup_attach_task_all(s->owner, current);
> -}
> -
> -static int vhost_attach_cgroups(struct vhost_dev *dev)
> -{
> - struct vhost_attach_cgroups_struct attach;
> -
> - attach.owner = current;
> - vhost_work_init(&attach.work, vhost_attach_cgroups_work);
> - vhost_work_queue(dev, &attach.work);
> - vhost_work_flush(dev, &attach.work);
> - return attach.ret;
> -}
> -
> /* Caller should have device mutex */
> bool vhost_dev_has_owner(struct vhost_dev *dev)
> {
> @@ -366,7 +360,6 @@ EXPORT_SYMBOL_GPL(vhost_dev_has_owner);
> /* Caller should have device mutex */
> long vhost_dev_set_owner(struct vhost_dev *dev)
> {
> - struct task_struct *worker;
> int err;
>
> /* Is there an owner already? */
> @@ -377,28 +370,15 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
>
> /* 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 */
> -
> - err = vhost_attach_cgroups(dev);
> - if (err)
> - goto err_cgroup;
>
> err = vhost_dev_alloc_iovecs(dev);
> if (err)
> - goto err_cgroup;
> + goto err_alloc;
>
> return 0;
> -err_cgroup:
> - kthread_stop(worker);
> +err_alloc:
> dev->worker = NULL;
> -err_worker:
> if (dev->mm)
> mmput(dev->mm);
> dev->mm = NULL;
> @@ -472,11 +452,6 @@ void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
> /* No one will access memory at this point */
> kfree(dev->memory);
> dev->memory = NULL;
> - WARN_ON(!list_empty(&dev->work_list));
> - if (dev->worker) {
> - kthread_stop(dev->worker);
> - dev->worker = NULL;
> - }
> if (dev->mm)
> mmput(dev->mm);
> dev->mm = NULL;
> @@ -1567,11 +1542,32 @@ EXPORT_SYMBOL_GPL(vhost_disable_notify);
>
> static int __init vhost_init(void)
> {
> + struct vhost_worker *w =
> + kzalloc(sizeof(*w), GFP_KERNEL);
> + if (!w)
> + return -ENOMEM;
> +
> + w->thread = kthread_create(vhost_worker,
> + w, "vhost-worker");
> + if (IS_ERR(w->thread))
> + return PTR_ERR(w->thread);
> +
> + worker = w;
> + spin_lock_init(&worker->work_lock);
> + INIT_LIST_HEAD(&worker->work_list);
> + wake_up_process(worker->thread);
> + pr_info("Created universal thread to service requests\n");
> +
> return 0;
> }
>
> static void __exit vhost_exit(void)
> {
> + if (worker) {
> + kthread_stop(worker->thread);
> + WARN_ON(!list_empty(&worker->work_list));
> + kfree(worker);
> + }
> }
>
> module_init(vhost_init);
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 8c1c792..2f204ce 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -22,6 +22,7 @@ struct vhost_work {
> int flushing;
> unsigned queue_seq;
> unsigned done_seq;
> + struct vhost_dev *dev;
> };
>
> /* Poll a file (eventfd or socket) */
> @@ -35,8 +36,8 @@ struct vhost_poll {
> struct vhost_dev *dev;
> };
>
> -void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn);
> -void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work);
> +void vhost_work_init(struct vhost_dev *dev,
> + struct vhost_work *work, vhost_work_fn_t fn);
>
> void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
> unsigned long mask, struct vhost_dev *dev);
> @@ -44,7 +45,6 @@ int 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);
> void vhost_poll_queue(struct vhost_poll *poll);
> -void vhost_work_flush(struct vhost_dev *dev, struct vhost_work *work);
> long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp);
>
> struct vhost_log {
> @@ -116,11 +116,22 @@ struct vhost_dev {
> int nvqs;
> struct file *log_file;
> struct eventfd_ctx *log_ctx;
> + /* vhost shared worker */
> + struct vhost_worker *worker;
> + /* for cgroup support */
> + struct task_struct *owner;
> +};
> +
> +struct vhost_worker {
> spinlock_t work_lock;
> struct list_head work_list;
> - struct task_struct *worker;
> + struct task_struct *thread;
> + struct task_struct *owner;
> };
>
> +void vhost_work_queue(struct vhost_worker *worker,
> + struct vhost_work *work);
> +void vhost_work_flush(struct vhost_worker *worker, struct vhost_work *work);
> void vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs, int nvqs);
> long vhost_dev_set_owner(struct vhost_dev *dev);
> bool vhost_dev_has_owner(struct vhost_dev *dev);
> --
> 2.4.3
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