netdev - Re: [Xen-devel] [PATCH] xen-netfront: correct MAX_TX

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Message-ID: <4F2BDA4C.7060601@redhat.com>
Date:	Fri, 03 Feb 2012 13:59:56 +0100
From:	Laszlo Ersek <lersek@...hat.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] [PATCH] xen-netfront: correct	MAX_TX_TARGET	calculation.

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
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