netdev - Re: [PATCH 1/4] net: skb_orphan on dev_hard_start

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Message-ID: <20090704074245.GA1615@gondor.apana.org.au>
Date:	Sat, 4 Jul 2009 15:42:45 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	rusty@...tcorp.com.au, patrick.ohly@...el.com,
	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	divy@...lsio.com, rolandd@...co.com, xemul@...nvz.org,
	dcbw@...hat.com, libertas-dev@...ts.infradead.org
Subject: Re: [PATCH 1/4] net: skb_orphan on dev_hard_start_xmit

On Fri, Jul 03, 2009 at 08:13:47PM -0700, David Miller wrote:
>
> NIU
> 
> I basically can't defer interrupts because the chip supports
> per-TX-desc interrupt indications but it lacks an "all TX queue sent"
> event.  So if, say, tell it to interrupt every 1/4 of the TX queue
> then up to 1/4 of the queue can have packets "stuck" in there
> if TX activity all of a sudden ceases.

Here's an idea: We let the sender decide whether we need to enable
notification.  This decision would be carried as a flag in the skb.
For example, UDP would set this flag when its socket buffer is close
to capacity.  Routing would set this flag per NAPI run, etc.

Of course you'd ignore this flag completely if the qdisc queue is
non-empty.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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