netdev - Re: [RFC v2 2/7] vhost_test: batch used buffer

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Date:   Thu, 25 Aug 2022 15:03:43 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Guo Zhi <qtxuning1999@...u.edu.cn>, eperezma@...hat.com,
        sgarzare@...hat.com, mst@...hat.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [RFC v2 2/7] vhost_test: batch used buffer


在 2022/8/17 21:57, Guo Zhi 写道:
> Only add to used ring when a batch of buffer have all been used.  And if
> in order feature negotiated, only add the last used descriptor for a
> batch of buffer.
>
> Signed-off-by: Guo Zhi <qtxuning1999@...u.edu.cn>
> ---
>   drivers/vhost/test.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
> index bc8e7fb1e635..57cdb3a3edf6 100644
> --- a/drivers/vhost/test.c
> +++ b/drivers/vhost/test.c
> @@ -43,6 +43,9 @@ struct vhost_test {
>   static void handle_vq(struct vhost_test *n)
>   {
>   	struct vhost_virtqueue *vq = &n->vqs[VHOST_TEST_VQ];
> +	struct vring_used_elem *heads = kmalloc(sizeof(*heads)
> +			* vq->num, GFP_KERNEL);


Though it's a test device, it would be better to try avoid memory 
allocation in the datapath.

And where is is freed?

Thanks


> +	int batch_idx = 0;
>   	unsigned out, in;
>   	int head;
>   	size_t len, total_len = 0;
> @@ -84,11 +87,14 @@ static void handle_vq(struct vhost_test *n)
>   			vq_err(vq, "Unexpected 0 len for TX\n");
>   			break;
>   		}
> -		vhost_add_used_and_signal(&n->dev, vq, head, 0);
> +		heads[batch_idx].id = cpu_to_vhost32(vq, head);
> +		heads[batch_idx++].len = cpu_to_vhost32(vq, len);
>   		total_len += len;
>   		if (unlikely(vhost_exceeds_weight(vq, 0, total_len)))
>   			break;
>   	}
> +	if (batch_idx)
> +		vhost_add_used_and_signal_n(&n->dev, vq, heads, batch_idx);
>   
>   	mutex_unlock(&vq->mutex);
>   }