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Date: Mon, 05 Apr 2010 10:35:11 -0700
From: Sridhar Samudrala <sri@...ibm.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Tom Lendacky <toml@...ibm.com>, netdev <netdev@...r.kernel.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH] vhost: Make it more scalable by creating a vhost
thread per device.
On Sun, 2010-04-04 at 14:14 +0300, Michael S. Tsirkin wrote:
> On Fri, Apr 02, 2010 at 10:31:20AM -0700, Sridhar Samudrala wrote:
> > Make vhost scalable by creating a separate vhost thread per vhost
> > device. This provides better scaling across multiple guests and with
> > multiple interfaces in a guest.
>
> Thanks for looking into this. An alternative approach is
> to simply replace create_singlethread_workqueue with
> create_workqueue which would get us a thread per host CPU.
>
> It seems that in theory this should be the optimal approach
> wrt CPU locality, however, in practice a single thread
> seems to get better numbers. I have a TODO to investigate this.
> Could you try looking into this?
Yes. I tried using create_workqueue(), but the results were not good
atleast when the number of guest interfaces is less than the number
of CPUs. I didn't try more than 8 guests.
Creating a separate thread per guest interface seems to be more
scalable based on the testing i have done so far.
I will try some more tests and get some numbers to compare the following
3 options.
- single vhost thread
- vhost thread per cpu
- vhost thread per guest virtio interface
Thanks
Sridhar
>
> >
> > I am seeing better aggregated througput/latency when running netperf
> > across multiple guests or multiple interfaces in a guest in parallel
> > with this patch.
>
> Any numbers? What happens to CPU utilization?
>
> > Signed-off-by: Sridhar Samudrala <sri@...ibm.com>
> >
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index a6a88df..29aa80f 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -339,8 +339,10 @@ static int vhost_net_open(struct inode *inode, struct file *f)
> > return r;
> > }
> >
> > - vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT);
> > - vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN);
> > + vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT,
> > + &n->dev);
> > + vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN,
> > + &n->dev);
> > n->tx_poll_state = VHOST_NET_POLL_DISABLED;
> >
> > f->private_data = n;
> > @@ -643,25 +645,14 @@ static struct miscdevice vhost_net_misc = {
> >
> > int vhost_net_init(void)
> > {
> > - int r = vhost_init();
> > - if (r)
> > - goto err_init;
> > - r = misc_register(&vhost_net_misc);
> > - if (r)
> > - goto err_reg;
> > - return 0;
> > -err_reg:
> > - vhost_cleanup();
> > -err_init:
> > - return r;
> > -
> > + return misc_register(&vhost_net_misc);
> > }
> > +
> > module_init(vhost_net_init);
> >
> > void vhost_net_exit(void)
> > {
> > misc_deregister(&vhost_net_misc);
> > - vhost_cleanup();
> > }
> > module_exit(vhost_net_exit);
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 7bd7a1e..243f4d3 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -36,8 +36,6 @@ enum {
> > VHOST_MEMORY_F_LOG = 0x1,
> > };
> >
> > -static struct workqueue_struct *vhost_workqueue;
> > -
> > static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
> > poll_table *pt)
> > {
> > @@ -56,18 +54,19 @@ static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
> > if (!((unsigned long)key & poll->mask))
> > return 0;
> >
> > - queue_work(vhost_workqueue, &poll->work);
> > + queue_work(poll->dev->wq, &poll->work);
> > return 0;
> > }
> >
> > /* Init poll structure */
> > void vhost_poll_init(struct vhost_poll *poll, work_func_t func,
> > - unsigned long mask)
> > + unsigned long mask, struct vhost_dev *dev)
> > {
> > INIT_WORK(&poll->work, func);
> > init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
> > init_poll_funcptr(&poll->table, vhost_poll_func);
> > poll->mask = mask;
> > + poll->dev = dev;
> > }
> >
> > /* Start polling a file. We add ourselves to file's wait queue. The caller must
> > @@ -96,7 +95,7 @@ void vhost_poll_flush(struct vhost_poll *poll)
> >
> > void vhost_poll_queue(struct vhost_poll *poll)
> > {
> > - queue_work(vhost_workqueue, &poll->work);
> > + queue_work(poll->dev->wq, &poll->work);
> > }
> >
> > static void vhost_vq_reset(struct vhost_dev *dev,
> > @@ -128,6 +127,11 @@ long vhost_dev_init(struct vhost_dev *dev,
> > struct vhost_virtqueue *vqs, int nvqs)
> > {
> > int i;
> > +
> > + dev->wq = create_singlethread_workqueue("vhost");
> > + if (!dev->wq)
> > + return -ENOMEM;
> > +
> > dev->vqs = vqs;
> > dev->nvqs = nvqs;
> > mutex_init(&dev->mutex);
> > @@ -143,7 +147,7 @@ long vhost_dev_init(struct vhost_dev *dev,
> > if (dev->vqs[i].handle_kick)
> > vhost_poll_init(&dev->vqs[i].poll,
> > dev->vqs[i].handle_kick,
> > - POLLIN);
> > + POLLIN, dev);
> > }
> > return 0;
> > }
> > @@ -216,6 +220,8 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> > if (dev->mm)
> > mmput(dev->mm);
> > dev->mm = NULL;
> > +
> > + destroy_workqueue(dev->wq);
> > }
> >
> > static int log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
> > @@ -1095,16 +1101,3 @@ void vhost_disable_notify(struct vhost_virtqueue *vq)
> > vq_err(vq, "Failed to enable notification at %p: %d\n",
> > &vq->used->flags, r);
> > }
> > -
> > -int vhost_init(void)
> > -{
> > - vhost_workqueue = create_singlethread_workqueue("vhost");
> > - if (!vhost_workqueue)
> > - return -ENOMEM;
> > - return 0;
> > -}
> > -
> > -void vhost_cleanup(void)
> > -{
> > - destroy_workqueue(vhost_workqueue);
> > -}
> > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > index 44591ba..60fefd0 100644
> > --- a/drivers/vhost/vhost.h
> > +++ b/drivers/vhost/vhost.h
> > @@ -29,10 +29,11 @@ struct vhost_poll {
> > /* struct which will handle all actual work. */
> > struct work_struct work;
> > unsigned long mask;
> > + struct vhost_dev *dev;
> > };
> >
> > void vhost_poll_init(struct vhost_poll *poll, work_func_t func,
> > - unsigned long mask);
> > + unsigned long mask, struct vhost_dev *dev);
> > void 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);
> > @@ -110,6 +111,7 @@ struct vhost_dev {
> > int nvqs;
> > struct file *log_file;
> > struct eventfd_ctx *log_ctx;
> > + struct workqueue_struct *wq;
> > };
> >
> > long vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue *vqs, int nvqs);
> > @@ -136,9 +138,6 @@ bool vhost_enable_notify(struct vhost_virtqueue *);
> > int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
> > unsigned int log_num, u64 len);
> >
> > -int vhost_init(void);
> > -void vhost_cleanup(void);
> > -
> > #define vq_err(vq, fmt, ...) do { \
> > pr_debug(pr_fmt(fmt), ##__VA_ARGS__); \
> > if ((vq)->error_ctx) \
> >
> >
> >
--
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