Messages in this thread | | | Date | Tue, 5 Mar 2013 16:46:41 -0500 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [PATCH RFC 12/12] xen-block: implement indirect descriptors |
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On Tue, Mar 05, 2013 at 06:07:57PM +0100, Roger Pau Monné wrote: > On 04/03/13 21:41, Konrad Rzeszutek Wilk wrote: > > On Thu, Feb 28, 2013 at 11:28:55AM +0100, Roger Pau Monne wrote: > >> Indirect descriptors introduce a new block operation > >> (BLKIF_OP_INDIRECT) that passes grant references instead of segments > >> in the request. This grant references are filled with arrays of > >> blkif_request_segment_aligned, this way we can send more segments in a > >> request. > >> > >> The proposed implementation sets the maximum number of indirect grefs > >> (frames filled with blkif_request_segment_aligned) to 256 in the > >> backend and 64 in the frontend. The value in the frontend has been > >> chosen experimentally, and the backend value has been set to a sane > >> value that allows expanding the maximum number of indirect descriptors > >> in the frontend if needed. > > > > So we are still using a similar format of the form: > > > > <gref, first_sec, last_sect, pad>, etc. > > > > Why not utilize a layout that fits with the bio sg? That way > > we might not even have to do the bio_alloc call and instead can > > setup an bio (and bio-list) with the appropiate offsets/list? > > > > Meaning that the format of the indirect descriptors is: > > > > <gref, offset, next_index, pad> > > > > We already know what the first_sec and last_sect are - they > > are basically: sector_number + nr_segments * (whatever the sector size is) + offset > > This will of course be suitable for Linux, but what about other OSes, I > know they support the traditional first_sec, last_sect (because it's > already implemented), but I don't know how much work will it be for them > to adopt this. If we have to do such a change I will have to check first > that other frontend/backend can handle this easily also, I wouldn't like > to simplify this for Linux by making it more difficult to implement in > other OSes...
I would think that most OSes use the same framework. The ones that are of notable interest are the Windows and BSD. Lets CC James here
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