netdev - Re: [PATCH net-next 3/3] mlx4_en: Saving mem access on data path

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Message-Id: <20120223.144749.1718133820851859801.davem@davemloft.net>
Date:	Thu, 23 Feb 2012 14:47:49 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	yevgenyp@...lanox.co.il
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 3/3] mlx4_en: Saving mem access on data path

From: Yevgeny Petrilin <yevgenyp@...lanox.co.il>
Date: Thu, 23 Feb 2012 15:34:44 +0200

> 
> Localized the pdev->dev, and using dma_map instead of pci_map
> There are multiple map/unmap operations on data path,
> optimizing those by saving redundant pointer access.
> 
> Signed-off-by: Yevgeny Petrilin <yevgenyp@...lanox.co.il>

I doubt you can measure any improvement from this at all, all of the
real cost is going to be in programming the hardware (both the
networking chip and potentially any IOMMU hardware to setup the DMA
mappings).  A pointer deref in of your datastructures will be
unnoticable.

When you make changes like this I want you to justify them with real
data and facts.

I think this entire patch set was in very poor taste and judgment.
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