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Date: Mon, 10 Aug 2015 16:09:29 -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
"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.
>> ---
>> 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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