Subject: Re: [Xen-devel] [PATCH] xen-netfront: correct MAX_TX_TARGET calculation.

From: Laszlo Ersek <[email-masked]>
Date: Fri, 03 Feb 2012 13:59:56 +0100

On 02/03/12 13:27, Laszlo Ersek wrote:
> On 01/27/12 11:36, Wei Liu wrote:

>> As the tx structure is bigger than rx structure. I think scratch space
>> size is likely to shrink after correction.
>
> It also seems to affect the netfront_tx_slot_available() function,
> making it stricter (likely). Before the patch, the function may have
> reported available slots when there were none, causing spurious(?) queue
> wakeups in xennet_maybe_wake_tx(), and not stopping the queue in
> xennet_start_xmit() when it should have(?).

(Eyeballing the source makes me think

   NET_TX_RING_SIZE == (4096 - 16 - 48) / (5 * 4) == 201
   NET_RX_RING_SIZE == (4096 - 16 - 48) / (4 * 4) == 252

but I didn't try to verify them.)

Laszlo