[RFC PATCH 1/4] vhost: Introduce a universal thread to serve all users

From: Bandan Das
Date: Mon Jul 13 2015 - 00:08:23 EST

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>
---
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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