-----Original Message-----
From: David Miller [mailto:davem@davemloft.net]
Sent: Tuesday, November 3, 2015 2:50 PM
To: Haiyang Zhang <haiyangz@microsoft.com>
Cc: eric.dumazet@gmail.com; KY Srinivasan <kys@microsoft.com>;
edumazet@google.com; netdev@vger.kernel.org
Subject: Re: [PATCH net-next] net: increase LL_MAX_HEADER if HYPERV_NET
is enabled

From: Haiyang Zhang <haiyangz@microsoft.com>
Date: Tue, 3 Nov 2015 18:49:05 +0000

quoted

quoted

-----Original Message-----
From: David Miller [mailto:davem@davemloft.net]
Sent: Tuesday, November 3, 2015 1:20 PM
To: Haiyang Zhang <haiyangz@microsoft.com>
Cc: eric.dumazet@gmail.com; KY Srinivasan <kys@microsoft.com>;
edumazet@google.com; netdev@vger.kernel.org
Subject: Re: [PATCH net-next] net: increase LL_MAX_HEADER if
HYPERV_NET is enabled

From: Haiyang Zhang <haiyangz@microsoft.com>
Date: Tue, 3 Nov 2015 17:34:47 +0000

quoted

But we still keep this busy return in our code, just for "weird corner

cases".

quoted

quoted

The queue_stopped condition must be precise.

The only case we return NETDEV_TX_BUSY is when the outgoing ring
buffer is full, which almost never happens because we stop the xmit queue

if ring is <10% available.

I don't think you understand.

You must perform the queue stop operation such that it is impossible for
your
->ndo_start_xmit() method to be invoked in a way such that you cannot
->transmit
the SKB given to you immediately.

We already did the queue stop operation in the netvsc_send_pkt() in file netvsc.c:
		if (ring_avail < RING_AVAIL_PERCENT_LOWATER) {
			netif_tx_stop_queue(netdev_get_tx_queue(ndev, q_idx));
This flow control mechanism stops the tx queue when the outgoing buffer on vmbus 
is <10% available. So we can always transmit immediately when start_xmit is called.

The case of returning NETDEV_TX_BUSY is not expected to happen normally.

Thanks,
- Haiyang

It's quite tiring to keep trying to explain this over and over repeatedly.