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

From: Paul Brook
Subject: Re: [Qemu-devel] buffer alignment for block backends
Date: Thu, 9 Apr 2009 16:38:51 +0100
User-agent: KMail/1.9.9

On Thursday 09 April 2009, Samuel Thibault wrote:
> 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.

Assuming that page == 4k is going to get you into all sorts of trouble.


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