netdev - Re: TCP performance regression

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Date:	Mon, 11 Nov 2013 21:43:51 +0530
From:	Sujith Manoharan <sujith@...jith.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Felix Fietkau <nbd@...nwrt.org>, netdev@...r.kernel.org,
	Dave Taht <dave.taht@...il.com>
Subject: Re: TCP performance regression

Eric Dumazet wrote:
> We have many choices.
> 
> 1) Add back a minimum of ~128 K of outstanding bytes per TCP session,
>    so that buggy drivers can sustain 'line rate'.
> 
>    Note that with 100 concurrent TCP streams, total amount of bytes
>    queued on the NIC is 12 MB.
>    And pfifo_fast qdisc will drop packets anyway.
> 
>    Thats what we call 'BufferBloat'
> 
> 2) Try lower values like 64K. Still bufferbloat.
> 
> 3) Fix buggy drivers, using a proper logic, or shorter timers (mvneta
> case for example)
> 
> 4) Add a new netdev attribute, so that well behaving NIC drivers do not
> have to artificially force TCP stack to queue too many bytes in
> Qdisc/NIC queues.

I think the quirks of 802.11 aggregation should be taken into account.
I am adding Felix to this thread, who would have more to say on latency/bufferbloat
with wireless drivers.

Sujith
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