Subject: Re: [TEST PATCH net-next] vhost: accumulate multiple used and sigal in vhost TX test

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 17 May 2011 23:52:45 +0300

On Tue, May 17, 2011 at 01:46:21PM -0700, Shirley Ma wrote:
> Hello Michael,
> 
> Here is the patch I used to test out of order before: add used in a pend
> array, and swap the last two ids. 
> 
> I used to hit an issue, but now it seems working well.

Aha, so if I apply this guest will *not* crash? :)

> This won't impact zero-copy patch since we need to maintain the pend
> used ids anyway.

Yes, but now we can mark them used immediately as they are
completed - and I am guessing this will relieve the
pressure on tx ring that you see?

> Signed-off-by: Shirley Ma <[email-masked]>
> ---
>  drivers/vhost/net.c   |   24 +++++++++++++++++++++++-
>  drivers/vhost/vhost.c |   11 +++++++++++
>  drivers/vhost/vhost.h |    1 +
>  3 files changed, 35 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 2f7c76a..19e1baa 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -32,6 +32,8 @@
>   * Using this limit prevents one virtqueue from starving others. */
>  #define VHOST_NET_WEIGHT 0x80000
>  
> +#define VHOST_MAX_PEND	128
> +
>  enum {
>  	VHOST_NET_VQ_RX = 0,
>  	VHOST_NET_VQ_TX = 1,
> @@ -198,13 +200,33 @@ static void handle_tx(struct vhost_net *net)
>  		if (err != len)
>  			pr_debug("Truncated TX packet: "
>  				 " len %d != %zd\n", err, len);
> -		vhost_add_used_and_signal(&net->dev, vq, head, 0);
> +		vq->heads[vq->pend_idx].id = head;
> +		vq->heads[vq->pend_idx].len = 0;
> +		++vq->pend_idx;
> +		if (vq->pend_idx >= VHOST_MAX_PEND) {
> +			int id;
> +			id = vq->heads[vq->pend_idx-1].id;
> +			vq->heads[vq->pend_idx-1].id = vq->heads[vq->pend_idx-2].id; 
> +			vq->heads[vq->pend_idx-2].id = id;
> +			vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
> +						    vq->pend_idx);
> +			vq->pend_idx = 0;
> +		}
>  		total_len += len;
>  		if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
>  			vhost_poll_queue(&vq->poll);
>  			break;
>  		}
>  	}
> +	if (vq->pend_idx >= VHOST_MAX_PEND) {
> +		int id;
> +		id = vq->heads[vq->pend_idx-1].id;
> +		vq->heads[vq->pend_idx-1].id = vq->heads[vq->pend_idx-2].id;
> +		vq->heads[vq->pend_idx-2].id = id;
> +		vhost_add_used_and_signal_n(&net->dev, vq, vq->heads,
> +					    vq->pend_idx);
> +		vq->pend_idx = 0;
> +	}
>  
>  	mutex_unlock(&vq->mutex);
>  }
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 2ab2912..7eea6b3 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -174,6 +174,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
>  	vq->call_ctx = NULL;
>  	vq->call = NULL;
>  	vq->log_ctx = NULL;
> +	vq->pend_idx = 0;
>  }
>  
>  static int vhost_worker(void *data)
> @@ -395,6 +396,11 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
>  			vhost_poll_stop(&dev->vqs[i].poll);
>  			vhost_poll_flush(&dev->vqs[i].poll);
>  		}
> +		if (dev->vqs[i].pend_idx != 0) {
> +			vhost_add_used_and_signal_n(dev, &dev->vqs[i],
> +				dev->vqs[i].heads, dev->vqs[i].pend_idx);
> +			dev->vqs[i].pend_idx = 0;
> +		}
>  		if (dev->vqs[i].error_ctx)
>  			eventfd_ctx_put(dev->vqs[i].error_ctx);
>  		if (dev->vqs[i].error)
> @@ -603,6 +609,11 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
>  
>  	mutex_lock(&vq->mutex);
>  
> +	if (vq->pend_idx != 0) {
> +		vhost_add_used_and_signal_n(d, vq, vq->heads, vq->pend_idx);
> +		vq->pend_idx = 0;
> +	}
> +
>  	switch (ioctl) {
>  	case VHOST_SET_VRING_NUM:
>  		/* Resizing ring with an active backend?
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index b3363ae..44a412d 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -108,6 +108,7 @@ struct vhost_virtqueue {
>  	/* Log write descriptors */
>  	void __user *log_base;
>  	struct vhost_log *log;
> +	int pend_idx;
>  };
>  
>  struct vhost_dev {
>