netdev - Re: TCP performance regression

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Date:	Mon, 11 Nov 2013 11:37:20 +0530
From:	Sujith Manoharan <sujith@...jith.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: TCP performance regression

Eric Dumazet wrote:
> I am afraid this commit shows bugs in various network drivers.
> 
> All drivers doing TX completion using a timer are buggy.
> 
> Holding skb 10 ms before TX completion is totally wrong and must be fixed.
> 
> If really NIC is not able to trigger an interrupt after TX completion, then
> driver should call skb_orphan() in its ndo_start_xmit()

802.11 AMPDU formation is done in the TX completion path in ath9k.

Incoming frames are added to a software queue and the TX completion
tasklet checks if enough frames are available to form an aggregate and
if so, forms new aggregates and transmits them.

There is no timer involved, but the completion routine is rather heavy.
Many wireless drivers handle 802.11 aggregation in this way:
ath9k, ath9k_htc, ath10k etc.

Sujith
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