Re: [Xen-devel] [RFC] netif: staging grants for requests

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Jan 04, 2017 at 11:40:21AM -0800, Stefano Stabellini wrote:
> On Wed, 14 Dec 2016, Joao Martins wrote:
> > # Proposed Extension
> > 
> > ## Terminology
> > 
> > `data gref` refers to the reusable/staging grants, whereas `gref` are the
> > ones that are granted/revoked for each packet being sent. `command ring`
> > refers to the current ring, whereas `data list` refers to the one proposed
> > below.
> > 
> > ## Xenstore
> > 
> > "feature-staging-grants" is a capability to allow the use of a set of
> > recycled buffers permanently mapped at the device setup. If
> > advertised, the frontend will grant a region equivalent to ```maximum number
> > of slots per ring * size of buffer``` where:
> > 
> >  * `maximum number of slots per ring` is the number of request structure
> >    that can be fit within the command ring. By default a request
> >    structure consumes 16 bytes. The first 64 bytes of a ring are used by
> >    producer and consumer indicies.
> 
> This means that by default the number of slots is (4096-64)/16 = 252,
> correct?
> 

The number needs to be rounded down to power of 2 IIRC, so it would be
128.

Wei.

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