netdev - Re: [PATCH net-next 7/8] vhost_net: try batch dequing from skb array

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Date:   Thu, 23 Mar 2017 13:34:36 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 7/8] vhost_net: try batch dequing from skb array



On 2017年03月22日 22:16, Michael S. Tsirkin wrote:
> On Tue, Mar 21, 2017 at 12:04:46PM +0800, Jason Wang wrote:
>> We used to dequeue one skb during recvmsg() from skb_array, this could
>> be inefficient because of the bad cache utilization and spinlock
>> touching for each packet. This patch tries to batch them by calling
>> batch dequeuing helpers explicitly on the exported skb array and pass
>> the skb back through msg_control for underlayer socket to finish the
>> userspace copying.
>>
>> Tests were done by XDP1:
>> - small buffer:
>>    Before: 1.88Mpps
>>    After : 2.25Mpps (+19.6%)
>> - mergeable buffer:
>>    Before: 1.83Mpps
>>    After : 2.10Mpps (+14.7%)
>>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>>   drivers/vhost/net.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++----
>>   1 file changed, 60 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index 9b51989..53f09f2 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -28,6 +28,8 @@
>>   #include <linux/if_macvlan.h>
>>   #include <linux/if_tap.h>
>>   #include <linux/if_vlan.h>
>> +#include <linux/skb_array.h>
>> +#include <linux/skbuff.h>
>>   
>>   #include <net/sock.h>
>>   
>> @@ -85,6 +87,7 @@ struct vhost_net_ubuf_ref {
>>   	struct vhost_virtqueue *vq;
>>   };
>>   
>> +#define VHOST_RX_BATCH 64
>>   struct vhost_net_virtqueue {
>>   	struct vhost_virtqueue vq;
>>   	size_t vhost_hlen;
>> @@ -99,6 +102,10 @@ struct vhost_net_virtqueue {
>>   	/* Reference counting for outstanding ubufs.
>>   	 * Protected by vq mutex. Writers must also take device mutex. */
>>   	struct vhost_net_ubuf_ref *ubufs;
>> +	struct skb_array *rx_array;
>> +	void *rxq[VHOST_RX_BATCH];
>> +	int rt;
>> +	int rh;
>>   };
>>   
>>   struct vhost_net {
>> @@ -201,6 +208,8 @@ static void vhost_net_vq_reset(struct vhost_net *n)
>>   		n->vqs[i].ubufs = NULL;
>>   		n->vqs[i].vhost_hlen = 0;
>>   		n->vqs[i].sock_hlen = 0;
>> +		n->vqs[i].rt = 0;
>> +		n->vqs[i].rh = 0;
>>   	}
>>   
>>   }
>> @@ -503,13 +512,30 @@ static void handle_tx(struct vhost_net *net)
>>   	mutex_unlock(&vq->mutex);
>>   }
>>   
>> -static int peek_head_len(struct sock *sk)
>> +static int peek_head_len_batched(struct vhost_net_virtqueue *rvq)
> Pls rename to say what it actually does: fetch skbs

Ok.

>
>> +{
>> +	if (rvq->rh != rvq->rt)
>> +		goto out;
>> +
>> +	rvq->rh = rvq->rt = 0;
>> +	rvq->rt = skb_array_consume_batched_bh(rvq->rx_array, rvq->rxq,
>> +						VHOST_RX_BATCH);
> A comment explaining why is is -bh would be helpful.

Ok.

Thanks