Re: [PATCH 2/2] vhost-net: revert vhost_exceeds_maxpend logic to its original

From: Jason Wang <jasowang@redhat.com>
To: Koichiro Den <den@klaipeden.com>, mst@redhat.com
Cc: netdev@vger.kernel.org, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 2/2] vhost-net: revert vhost_exceeds_maxpend logic to its original
Date: Mon, 21 Aug 2017 11:06:33 +0800	[thread overview]
Message-ID: <0cbc33d6-eb1e-cea4-4cdf-a8a88932da62@redhat.com> (raw)
In-Reply-To: <20170819064129.27272-1-den@klaipeden.com>

On 2017年08月19日 14:41, Koichiro Den wrote:
> To depend on vq.num and the usage of VHOST_MAX_PEND is not succinct
> and in some case unexpected, so revert its logic part only.

Hi:

Could you explain a little bit more on the case that is was not sufficent?

Thanks

>
> Signed-off-by: Koichiro Den <den@klaipeden.com>
> ---
>   drivers/vhost/net.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 06d044862e58..99cf99b308a7 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -433,11 +433,15 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
>   
>   static bool vhost_exceeds_maxpend(struct vhost_net *net)
>   {
> +	int num_pends;
>   	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
>   	struct vhost_virtqueue *vq = &nvq->vq;
>   
> -	return (nvq->upend_idx + vq->num - VHOST_MAX_PEND) % UIO_MAXIOV
> -		== nvq->done_idx;
> +	num_pends = likely(nvq->upend_idx >= nvq->done_idx) ?
> +		(nvq->upend_idx - nvq->done_idx) :
> +		(nvq->upend_idx + UIO_MAXIOV - nvq->done_idx);
> +
> +	return num_pends > VHOST_MAX_PEND;
>   }
>   
>   /* Expects to be always run from workqueue - which acts as

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