RE: [Xen-devel] swiotlb and Xen query?

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: pradeep singh rautela [mailto:rautelap@xxxxxxxxx] 
> Sent: 03 May 2007 10:25
> To: Petersson, Mats
> Cc: xen-devel
> Subject: Re: [Xen-devel] swiotlb and Xen query?
> 
> 
> 
> On 5/3/07, Petersson, Mats <Mats.Petersson@xxxxxxx> wrote:
> 
>       [snip]
>       >
>       >
>       > That was really very informative Mats.
>       > Thanks you very much for the help.
>       > So, i guess swiotlb comes into picture only if there is a DMA
>       > transfer from a domU whose p2m mapping turns out to be above 
>       > the 4GB( assuming device to be 32 bit) of the machine memory.
>       > Other wise just normal p2m mapping is enough to find the
>       > actual machine address, which can be handed over to the
>       > device for DMAing. Am i right? 
>       
>       Yes, that's pretty much how it works. In theory, it 
> could be that
>       devices only work on a 31, 28 or some other number of 
> bit-range, but
>       yes, that's the principle.
> 
> 
> Ok.Got this correct. 
> I am sure this can cause problems while migrating live 
> domains across cpus.
> yes/no/thoughts?

Yes, you can't live-migrate (or migrate at all, I think) driver domains,
as there is no way to determine if a driver has outstanding DMA
requests. You need to shut it down and restart it elsewhere if you want
to move it from one machine to another. [Of course not across CPU's, but
if you actually move across physical machine boundary]. 

[I had a quick look, but I couldn't actually find any checks for this,
but I still believe it holds true that driver domains can't be
saved/restored/migrated]. 

--
Mats
> 
> Thank you 
> ~psr
> 
> 
> 
>       --
>       Mats
>       >
>       > Thank you once again for the patience.
>       >
>       > Regards
>       > ~psr
>       >
>       [snip]
>       
>       
>       
> 
> 
> 
> 
> -- 
> ---
> pradeep singh rautela
> 
> "Genius is 1% inspiration, and 99% perspiration" - not me :) 
> 



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