From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: Writing to a ramdisk in a PV domain is SLLLOOOWWW?!?
Date: Thu, 06 May 2010 15:26:10 -0700
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To: "Santos, Jose Renato G" <joserenato.santos@hp.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>, "Xen-Devel (xen-devel@lists.xensource.com)" <xen-devel@lists.xensource.com>
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On 05/06/2010 03:04 PM, Santos, Jose Renato G wrote:
> This is complete wild guess, but could it be that you are doing multi-page I/O with non contiguous machine pages?
> I believe the DMA API for pv guests uses swioltlb which does extra copies to a bounce buffer if you request a dma address to a multi-page region (as the pages may be non contiguous).
>   

Ramdisk access shouldn't be going anywhere near DMA API or swiotlb.

    J