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Date: Sun, 4 Apr 2010 14:14:33 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Sridhar Samudrala <sri@...ibm.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 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?
>
> 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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