netdev - Re: [PATCH 2.6.25 1/1]S2io: Multiqueue network device support implementation

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Date:	Wed, 23 Jan 2008 23:30:06 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	andi@...stfloor.org
Cc:	Ramkrishna.Vepa@...erion.com, Sreenivasa.Honnur@...erion.com,
	netdev@...r.kernel.org, jeff@...zik.org, support@...erion.com
Subject: Re: [PATCH 2.6.25 1/1]S2io: Multiqueue network device support
 implementation

From: Andi Kleen <andi@...stfloor.org>
Date: Thu, 24 Jan 2008 08:25:49 +0100

> > have done away with handling tx completion in the interrupt handler, and
> > are instead handling them in the context of the transmit. The slow path,
> > straggling transmit completions will be handled in the timer context.
> 
> Ok -- hopefully you don't have bad corner cases from this when the pipe
> is not fully filled and then causing longer latencies on completion. 
> Old NAPI sometimes suffered from such problems. 

BTW, such a TX completion timer will stall TCP sockets when the TX
queue of the device is partially filled and then sending stops.

TX ring SKB liberation really must be done in a very small finite
amount of time in order to avoid this problem properly.

Deferring it to HZ granular timers doesn't give a quick enough
response, especially at high packet rates.
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