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Date: Fri, 17 Feb 2012 17:02:05 -0600
From: Anthony Liguori <aliguori@...ibm.com>
To: netdev@...r.kernel.org
Cc: Michael Tsirkin <mst@...hat.com>,
Anthony Liguori <aliguori@...ibm.com>,
Tom Lendacky <toml@...ibm.com>,
Cristian Viana <vianac@...ibm.com>
Subject: [PATCH 1/2] vhost: allow multiple workers threads
This patch allows vhost to have multiple worker threads for devices such as
virtio-net which may have multiple virtqueues.
Since virtqueues are a lockless ring queue, in an ideal world data is being
produced by the producer as fast as data is being consumed by the consumer.
These loops will continue to consume data until none is left.
vhost currently multiplexes the consumer side of the queue on a single thread
by attempting to read from the queue until everything is read or it cannot
process anymore. This means that activity on one queue may stall another queue.
This is exacerbated when using any form of polling to read from the queues (as
we'll introduce in the next patch). By spawning a thread per-virtqueue, this
is addressed.
The only problem with this patch right now is how the wake up of the threads is
done. It's essentially a broadcast and we have seen lock contention as a
result. We've tried some approaches to signal a single thread but I'm not
confident that that code is correct yet so I'm only sending the broadcast
version.
Here are some performance results from this change. There's a modest
improvement with stream although a fair bit of variability too.
With RR, there's pretty significant improvements as the instance rate drives up.
Test, Size, Instance, Baseline, Patch, Relative
TCP_RR
Tx:256 Rx:256
1 9,639.66 10,164.06 105.44%
10 62,819.55 54,059.78 86.06%
30 84,715.60 131,241.86 154.92%
60 124,614.71 148,720.66 119.34%
UDP_RR
Tx:256 Rx:256
1 9,652.50 10,343.72 107.16%
10 53,830.26 58,235.90 108.18%
30 89,471.01 97,634.53 109.12%
60 103,640.59 164,035.01 158.27%
TCP_STREAM
Tx: 256
1 2,622.63 2,610.71 99.55%
4 4,928.02 4,812.05 97.65%
Tx: 1024
1 5,639.89 5,751.28 101.97%
4 5,874.72 6,575.55 111.93%
Tx: 4096
1 6,257.42 7,655.22 122.34%
4 5,370.78 6,044.83 112.55%
Tx: 16384
1 6,346.63 7,267.44 114.51%
4 5,198.02 5,657.12 108.83%
TCP_MAERTS
Rx: 256
1 2,091.38 1,765.62 84.42%
4 5,319.52 5,619.49 105.64%
Rx: 1024
1 7,030.66 7,593.61 108.01%
4 9,040.53 7,275.84 80.48%
Rx: 4096
1 9,160.93 9,318.15 101.72%
4 9,372.49 8,875.63 94.70%
Rx: 16384
1 9,183.28 9,134.02 99.46%
4 9,377.17 8,877.52 94.67%
106.46%
Cc: Tom Lendacky <toml@...ibm.com>
Cc: Cristian Viana <vianac@...ibm.com>
Signed-off-by: Anthony Liguori <aliguori@...ibm.com>
---
drivers/vhost/net.c | 6 ++++-
drivers/vhost/vhost.c | 51 ++++++++++++++++++++++++++++++------------------
drivers/vhost/vhost.h | 8 +++++-
3 files changed, 43 insertions(+), 22 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 9dab1f5..47175cd 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -33,6 +33,10 @@ static int experimental_zcopytx;
module_param(experimental_zcopytx, int, 0444);
MODULE_PARM_DESC(experimental_zcopytx, "Enable Experimental Zero Copy TX");
+static int workers = 2;
+module_param(workers, int, 0444);
+MODULE_PARM_DESC(workers, "Set the number of worker threads");
+
/* Max number of bytes transferred before requeueing the job.
* Using this limit prevents one virtqueue from starving others. */
#define VHOST_NET_WEIGHT 0x80000
@@ -504,7 +508,7 @@ static int vhost_net_open(struct inode *inode, struct file *f)
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(dev, n->vqs, VHOST_NET_VQ_MAX);
+ r = vhost_dev_init(dev, n->vqs, workers, VHOST_NET_VQ_MAX);
if (r < 0) {
kfree(n);
return r;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c14c42b..676cead 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -144,9 +144,12 @@ static inline void vhost_work_queue(struct vhost_dev *dev,
spin_lock_irqsave(&dev->work_lock, flags);
if (list_empty(&work->node)) {
+ int i;
+
list_add_tail(&work->node, &dev->work_list);
work->queue_seq++;
- wake_up_process(dev->worker);
+ for (i = 0; i < dev->nworkers; i++)
+ wake_up_process(dev->workers[i]);
}
spin_unlock_irqrestore(&dev->work_lock, flags);
}
@@ -287,7 +290,7 @@ static void vhost_dev_free_iovecs(struct vhost_dev *dev)
}
long vhost_dev_init(struct vhost_dev *dev,
- struct vhost_virtqueue *vqs, int nvqs)
+ struct vhost_virtqueue *vqs, int nworkers, int nvqs)
{
int i;
@@ -300,7 +303,9 @@ long vhost_dev_init(struct vhost_dev *dev,
dev->mm = NULL;
spin_lock_init(&dev->work_lock);
INIT_LIST_HEAD(&dev->work_list);
- dev->worker = NULL;
+ dev->nworkers = min(nworkers, VHOST_MAX_WORKERS);
+ for (i = 0; i < dev->nworkers; i++)
+ dev->workers[i] = NULL;
for (i = 0; i < dev->nvqs; ++i) {
dev->vqs[i].log = NULL;
@@ -354,7 +359,7 @@ static int vhost_attach_cgroups(struct vhost_dev *dev)
static long vhost_dev_set_owner(struct vhost_dev *dev)
{
struct task_struct *worker;
- int err;
+ int err, i;
/* Is there an owner already? */
if (dev->mm) {
@@ -364,28 +369,34 @@ static 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;
- }
+ for (i = 0; i < dev->nworkers; i++) {
+ worker = kthread_create(vhost_worker, dev, "vhost-%d.%d", current->pid, i);
+ if (IS_ERR(worker)) {
+ err = PTR_ERR(worker);
+ goto err_worker;
+ }
- dev->worker = worker;
- wake_up_process(worker); /* avoid contributing to loadavg */
+ dev->workers[i] = worker;
+ wake_up_process(worker); /* avoid contributing to loadavg */
+ }
err = vhost_attach_cgroups(dev);
if (err)
- goto err_cgroup;
+ goto err_worker;
err = vhost_dev_alloc_iovecs(dev);
if (err)
- goto err_cgroup;
+ goto err_worker;
return 0;
-err_cgroup:
- kthread_stop(worker);
- dev->worker = NULL;
+
err_worker:
+ for (i = 0; i < dev->nworkers; i++) {
+ if (dev->workers[i]) {
+ kthread_stop(dev->workers[i]);
+ dev->workers[i] = NULL;
+ }
+ }
if (dev->mm)
mmput(dev->mm);
dev->mm = NULL;
@@ -475,9 +486,11 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
lockdep_is_held(&dev->mutex)));
RCU_INIT_POINTER(dev->memory, NULL);
WARN_ON(!list_empty(&dev->work_list));
- if (dev->worker) {
- kthread_stop(dev->worker);
- dev->worker = NULL;
+ for (i = 0; i < dev->nworkers; i++) {
+ if (dev->workers[i]) {
+ kthread_stop(dev->workers[i]);
+ dev->workers[i] = NULL;
+ }
}
if (dev->mm)
mmput(dev->mm);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index a801e28..fa5e75e 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -18,6 +18,9 @@
#define VHOST_DMA_DONE_LEN 1
#define VHOST_DMA_CLEAR_LEN 0
+/* Maximum number of worker threads per-vhost device */
+#define VHOST_MAX_WORKERS 8
+
struct vhost_device;
struct vhost_work;
@@ -157,10 +160,11 @@ struct vhost_dev {
struct eventfd_ctx *log_ctx;
spinlock_t work_lock;
struct list_head work_list;
- struct task_struct *worker;
+ int nworkers;
+ struct task_struct *workers[VHOST_MAX_WORKERS];
};
-long vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue *vqs, int nvqs);
+long vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue *vqs, int nworkers, int nvqs);
long vhost_dev_check_owner(struct vhost_dev *);
long vhost_dev_reset_owner(struct vhost_dev *);
void vhost_dev_cleanup(struct vhost_dev *);
--
1.7.4.1
--
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