netdev - Re: [PATCH 3/4 v2 net-next] net: make GRO aware of skb->head

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Date:	Wed, 02 May 2012 04:45:03 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	Alexander Duyck <alexander.duyck@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Tom Herbert <therbert@...gle.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Michael Chan <mchan@...adcom.com>,
	Matt Carlson <mcarlson@...adcom.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	Maciej Żenczykowski <maze@...gle.com>
Subject: Re: [PATCH 3/4 v2 net-next] net: make GRO aware of skb->head_frag

On Tue, 2012-05-01 at 12:45 -0700, Alexander Duyck wrote:

> I wasn't worried about the kfree vs put_page, I was worried about the
> coalesce case.  However, it looks like you are correct and I am not
> seeing any issues so everything seems to be working fine.
> 
> I have a hacked together ixgbe up and running now with the new build_skb
> logic and RSC/LRO disabled.  It looks like it is giving me a 5%
> performance boost for small packet routing, but I am using more CPU for
> netperf TCP receive tests and I was wondering if you had seen anything
> similar on the tg3 driver?
> 



Hmm, tg3 perf for small packets is not changed, because tg3 uses
copybreak anyway.

#define TG3_RX_COPY_THRESHOLD       256

For big packets, I have no changes in netperf because GRO cannot really
provide big enough skbs at 1Gb speed.

The changes are noticeable when BDP (Bandwidth*Delay Product) is large
and some packet losses happen : You notice lower latencies in TCP stack,
because of less collapses (big copies)



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