netdev - Re: [PATCH V2 net-next 1/1] hv_netvsc: Use the xmit_more skb flag to optimize signaling the host

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Date:	Thu, 30 Apr 2015 21:36:35 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	olaf@...fle.de, apw@...onical.com, jasowang@...hat.com
Subject: Re: [PATCH V2 net-next 1/1] hv_netvsc: Use the xmit_more skb flag
 to optimize signaling the host

On Thu, 2015-04-30 at 16:29 -0700, K. Y. Srinivasan wrote:
> Based on the information given to this driver (via the xmit_more skb flag),
> we can defer signaling the host if more packets are on the way. This will help
> make the host more efficient since it can potentially process a larger batch of
> packets. Implement this optimization.
> 
> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> ---
> 	v2: Fixed up indentation based on feedback from David Miller.
> 
>  drivers/net/hyperv/netvsc.c |   20 ++++++++++++--------
>  1 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
> index 2e8ad06..5fdc5e1 100644
> --- a/drivers/net/hyperv/netvsc.c
> +++ b/drivers/net/hyperv/netvsc.c
> @@ -743,6 +743,7 @@ static inline int netvsc_send_pkt(
>  	u64 req_id;
>  	int ret;
>  	struct hv_page_buffer *pgbuf;
> +	u32 vmbus_flags = VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED;
>  
>  	nvmsg.hdr.msg_type = NVSP_MSG1_TYPE_SEND_RNDIS_PKT;
>  	if (packet->is_data_pkt) {
> @@ -772,19 +773,22 @@ static inline int netvsc_send_pkt(
>  	if (packet->page_buf_cnt) {
>  		pgbuf = packet->cp_partial ? packet->page_buf +
>  			packet->rmsg_pgcnt : packet->page_buf;
> -		ret = vmbus_sendpacket_pagebuffer(out_channel,
> -						  pgbuf,
> -						  packet->page_buf_cnt,
> -						  &nvmsg,
> -						  sizeof(struct nvsp_message),
> -						  req_id);
> +		ret = vmbus_sendpacket_pagebuffer_ctl(out_channel,
> +						      pgbuf,
> +						      packet->page_buf_cnt,
> +						      &nvmsg,
> +						      sizeof(struct
> +							     nvsp_message),
> +						      req_id,
> +						      vmbus_flags,
> +						      !packet->xmit_more);
>  	} else {
> -		ret = vmbus_sendpacket(
> +		ret = vmbus_sendpacket_ctl(
>  				out_channel, &nvmsg,
>  				sizeof(struct nvsp_message),
>  				req_id,
>  				VM_PKT_DATA_INBAND,
> -				VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> +				vmbus_flags, !packet->xmit_more);
>  	}
>  
>  	if (ret == 0) {

This might be problematic, if queue is stopped ( netif_tx_stop_queue())

You need to force a kick if we are about to stop the queue :

Random example : commit ddd0ca5d60b350bbfbfb60b25885a9779ce6d6c7



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