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Date: Mon, 10 Aug 2015 17:05:13 -0400
From: Bandan Das <bsd@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: kvm@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, Eyal Moscovici <EYALMO@...ibm.com>,
Razya Ladelsky <RAZYA@...ibm.com>, cgroups@...r.kernel.org,
jasowang@...hat.com
Subject: Re: [RFC PATCH 1/4] vhost: Introduce a universal thread to serve all users
Bandan Das <bsd@...hat.com> writes:
> "Michael S. Tsirkin" <mst@...hat.com> writes:
>
>> 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@...ibm.com>
>>> Signed-off-by: Bandan Das <bsd@...hat.com>
>>
>> BTW, how does this interact with virtio net MQ?
>> It would seem that MQ gains from more parallelism and
>> CPU locality.
>
> Hm.. Good point. As of this version, this design will always have
> one worker thread servicing a guest. Now suppose we have 10 virtio
> queues for a guest, surely, we could benefit from spawning off another
> worker just like we are doing in case of a new guest/device with
> the devs_per_worker parameter.
So, I did a quick smoke test with virtio-net and the Elvis patches.
virtio net MQ already spawns a new worker thread for every queue,
it seems ? So, the above setup already works! :) I will run some tests and
post back the results.
>>> ---
>>> 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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