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

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Message-ID: <OF1B3705AA.30E31D1D-ON652575DD.001F2CCD-652575DD.001FAE94@in.ibm.com>
Date:	Mon, 22 Jun 2009 11:16:03 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>,
	Matt Carlson <mcarlson@...adcom.com>, netdev@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 2/4] virtio_net: return NETDEV_TX_BUSY instead of	queueing an
 extra skb.

Hi Herbert,

> Herbert Xu <herbert@...dor.apana.org.au> wrote on 06/19/2009 10:06:13 AM:
>
> > We either remove the API, or fix it.  I think fixing it is better,
because my
> > driver will be simpler and it's obvious noone wants to rewrite 50
drivers and
> > break several of them.
>
> My preference is obviously in the long term removal of TX_BUSY.
> Due to resource constraints that cannot be done immediately.  So
> at least we should try to stop its proliferation.
>
> BTW removing TX_BUSY does not mean that your driver has to stay
> complicated.  As I have said repeatedly your driver should be
> checking the stop-queue condition after transmission, not before.
>
> In fact queueing it in the driver is just as bad as return TX_BUSY!

I was curious about "queueing it in the driver" part: why is this bad? Do
you
anticipate any performance problems, or does it break QoS, or something
else I
have missed?

thanks,

- KK

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