[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH RFC 12/12] xen-block: implement indirect descriptors



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...


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.