netdev - Re: [PATCH v2] tcp: splice as many packets as possible at once

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Message-Id: <20090127.104210.136585415.davem@davemloft.net>
Date:	Tue, 27 Jan 2009 10:42:10 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	zbr@...emap.net
Cc:	jarkao2@...il.com, herbert@...dor.apana.org.au, w@....eu,
	dada1@...mosbay.com, ben@...s.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: [PATCH v2] tcp: splice as many packets as possible at once

From: David Miller <davem@...emloft.net>
Date: Mon, 26 Jan 2009 22:10:56 -0800 (PST)

> Even for drivers like NIU and myri10ge that do this, they only
> use heuristics or some fixed minimum to decide how much to
> move to the linear area.
> 
> Result?  Some data payload bits end up there because it overshoots.
 ...
> I did test this with the NIU driver at one point, and it did not
> change TCP latency nor throughput at all even at 10g speeds.

As a followup, it turns out that NIU right now does this properly.

It only pulls a maximum of ETH_HLEN into the linear area before giving
the SKB to netif_receive_skb().
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