Re: [Xen-devel] [PATCH] xen: blkif.h: document linux xen-block multi-page ring implementation

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, May 15, 2015 at 04:38:58PM +0100, Jan Beulich wrote:
> >>> On 15.05.15 at 17:22, <konrad.wilk@xxxxxxxxxx> wrote:
> > Doing an git annotate shows:
> > 
> > commit 829f2a9c6dfae13faee4e24b953441113338e0f2
> > Author: Justin T. Gibbs <justing@xxxxxxxxxxxxxxxx>
> > Date:   Thu Feb 23 10:02:30 2012 +0000
> > 
> >     blkif.h: Document the Red Hat and Citrix blkif multi-page ring 
> > extensions
> >     
> >     No functional changes.
> > 
> > 
> > Which says:
> > 
> >  * (1) Multi-page ring buffer scheme first developed in the Citrix XenServer
> > + *     PV drivers.
> > + * (2) Multi-page ring buffer scheme first used in some RedHat 
> > distributions
> > + *     including a distribution deployed on certain nodes of the Amazon
> > + *     EC2 cluster.
> > + * (3) Support for multi-page ring buffers was implemented independently,
> > + *     in slightly different forms, by both Citrix and RedHat/Amazon.
> > 
> > 
> > And I double checked the linux-2.6.18.hg tree and I see no mention of 
> > multi-page. I wonder where such code exists?
> 
> We have support for multi page rings in our kernels, largely because
> (iirc) Amazon had asked it.

Aha!

Bob has found that he can use 'ring-page-order' and 'max-ring-page-order'
which are the new standard and not have to worry about breaking older
guests.
> 
> Jan
> 

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