netdev - RE: [PATCH 3/7] mlx4_en: Incoming traffic alignment optimizations

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Date:	Tue, 18 Oct 2011 07:43:08 +0000
From:	Yevgeny Petrilin <yevgenyp@...lanox.co.il>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 3/7] mlx4_en: Incoming traffic alignment optimizations

> 
> > @@ -91,7 +91,7 @@
> >  /* Receive fragment sizes; we use at most 4 fragments (for 9600 byte MTU
> >   * and 4K allocations) */
> >  enum {
> > -	FRAG_SZ0 = 512 - NET_IP_ALIGN,
> > +	FRAG_SZ0 = 2048,
> >  	FRAG_SZ1 = 1024,
> >  	FRAG_SZ2 = 4096,
> >  	FRAG_SZ3 = MLX4_EN_ALLOC_SIZE
> 
> Is the 512 -> 2048 change really wanted ? Its not mentioned in changelog and is confusing.
> 
> This means mlx4 lost the ability to use a small frag (512 bytes) to store small frames.
> 
The change is wanted as an optimization for our HW.
We do get better numbers with this change, even with small packets.
You are correct, I should have mentioned it in the changelog.

Yevgeny