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Re: [Qemu-devel] buffer alignment for block backends

From: Samuel Thibault
Subject: Re: [Qemu-devel] buffer alignment for block backends
Date: Thu, 9 Apr 2009 17:19:44 +0200
User-agent: Mutt/1.5.12-2006-07-14

Anthony Liguori, le Thu 09 Apr 2009 08:11:27 -0500, a écrit :
> >- ide.c:ide_init2
> >  
> This buffer is only used when not doing DMA.  When doing DMA, we are 
> able to do zero-copy IO so the alignment of the request depends on how 
> the guest aligned the request.  I suspect you'll find a lot of guests 
> that, in practice, do not align requests at 4k boundaries.

Eeeeerrr, why shoudn't they?  Guests usually work on pages, which are
already aligned on 4k boundaries.

> I don't know what the requirements are for IDE but I would be
> surprised if it was 4k.

I believe there is no requirement.


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