netdev - Re: [PATCH net-next] net: more accurate skb truesize

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Message-ID: <1318523564.2745.32.camel@bwh-desktop>
Date:	Thu, 13 Oct 2011 17:32:44 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH net-next] net: more accurate skb truesize

On Thu, 2011-10-13 at 18:24 +0200, Eric Dumazet wrote:
> Le jeudi 13 octobre 2011 à 17:05 +0100, Ben Hutchings a écrit :
[...]
> > If that's not important, and we just want to be sure that the allocation
> > occupies at least a whole cache line, then it should be:
> > 	size = SKB_DATA_ALIGN(size + sizeof(struct skb_shared_info));
> > 
> > But I don't think it makes sense to use SKB_DATA_ALIGN(sizeof(struct
> > skb_shared_info)).
> 
> If you take a closer look, you'll see that my patch addresses your
> concerns, but at minimal cpu cost.
> 
> kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
> 
> will give same result than :
> 
> kmalloc(SKB_DATA_ALIGN(size) + SKB_DATA_ALIGN(sizeof(struct
> skb_shared_info)))
> 
> But my version is a bit faster (a single add of a compiler known
> constant)

Fair enough, but please add a comment explaining this.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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