netdev - Re: [PATCH] mlx4_en: map entire pages to increase throughput

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Date:	Mon, 16 Jul 2012 22:29:03 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	rick.jones2@...com
Cc:	cascardo@...ux.vnet.ibm.com, netdev@...r.kernel.org,
	yevgenyp@...lanox.co.il, ogerlitz@...lanox.com, amirv@...lanox.com,
	brking@...ux.vnet.ibm.com, leitao@...ux.vnet.ibm.com,
	klebers@...ux.vnet.ibm.com
Subject: Re: [PATCH] mlx4_en: map entire pages to increase throughput

From: Rick Jones <rick.jones2@...com>
Date: Mon, 16 Jul 2012 10:27:57 -0700

> That seems rather extraordinarily low - Power7 is supposed to be a
> rather high performance CPU.  The last time I noticed O(3Gbit/s) on
> 10G for bulk transfer was before the advent of LRO/GRO - that was in
> the x86 space though.  Is mapping really that expensive with Power7?

Unfortunately, IOMMU mappings are incredibly expensive.  I see effects
like this on Sparc too.
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