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

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Date:	Tue, 18 Oct 2011 08:52:03 +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

> 
> Oh my...
> 
> Of course you are aware that the 'truesize' stuff around means that using big frag size will probably lower your performance number, unless you allow protocol stacks to use more ram ?
> 
> Only possible drawback using 512 bytes instead of 2048 is the cache-line bounce on the page->_count field. So I would say your change hides a performance issue of your driver.
> 
> Maybe you should make sure you dont touch it too often [ You should use a single add per allocated PAGE, not 2 (for 2048-bytes frags) or 8 (for 512-bytes frags) ]
> 
> 
Thanks Eric,
I'll check this.
In the meanwhile will resubmit the series without this change.