netdev - Re: [PATCH net-next 09/11] sfc: Prefetch RX skb header area

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Date:	Wed, 19 Jun 2013 15:56:21 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-net-drivers@...arflare.com
Subject: Re: [PATCH net-next 09/11] sfc: Prefetch RX skb header area

On Wed, 2013-06-19 at 23:39 +0100, Ben Hutchings wrote:

> You can't use build_skb() if you put multiple RX buffers in a page.  See
> <1365805319.2791.18.camel@...-desktop.uk.solarflarecom.com>.

Well, you use small skb (used to have 64 bytes headroom and you changed
it to 128) and attach a frag on it, so anyway build_skb() brings
nothing.

I suspect you have a win on workloads with flood of rx, but on moderate
load sk_buff will be cold, so the cache adds latencies.

My feeling is that this kind of tradeoff should not be per driver.

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