netdev - Re: [PATCH 2/4] virtio_net: return NETDEV_TX_BUSY instead of queueing an extra skb.

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Message-Id: <200906221209.16481.rusty@rustcorp.com.au>
Date:	Mon, 22 Jun 2009 12:09:15 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	David Miller <davem@...emloft.net>,
	Matt Carlson <mcarlson@...adcom.com>
Subject: Re: [PATCH 2/4] virtio_net: return NETDEV_TX_BUSY instead of queueing an extra skb.

On Fri, 19 Jun 2009 11:40:14 pm Herbert Xu wrote:
> > On the other hand, we're underutilizing the queue to avoid it.  I find
> > that a little embarrassing.
>
> Here's why I think this is not an issue.  If your NIC is high
> bandwidth then your ring is going to have to be huge so the
> amount that is underutilised (a 64K packet) is tiny.  If your
> NIC is low bandwidth then this is where you often need QoS and
> in that case you do *NOT* want to fully utilise the HW queue.

Well, we leave that up to the NIC designer.  It's retro-justification for 
throwing away a few percent of the queue, but the QoS issue is even more in 
the noise.

But I will give in now and change virtio_net to use this substandard API :(

Thanks,
Rusty.
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