Messages in this thread | | | Subject | Re: [PATCH 0/7] sg_ring: a ring of scatterlist arrays | From | James Bottomley <> | Date | Sat, 05 Jan 2008 09:31:12 -0600 |
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On Wed, 2007-12-19 at 17:31 +1100, Rusty Russell wrote: > This patch series is the start of my attempt to simplify and make explicit > the chained scatterlist logic. > > It's not complete: my SATA box boots and seems happy, but all the other > users of SCSI need to be updated and checked. But I've gotten far enough > to believe it's worth persuing.
Sorry for the delay in looking at this, I was busy with Holidays and things.
When I compare sg_ring with the current sg_chain (and later sg_table) implementations, I'm actually struck by how similar they are.
The other thing I note is that the problem you're claiming to solve with sg_ring (the ability to add extra scatterlists to the front or the back of an existing one) is already solved with sg_chain, so the only real advantage of sg_ring was that it contains explicit counts, which sg_table (in -mm) also introduces.
The other differences are that sg_ring only allows adding at the front or back of an existing sg_ring, it doesn't allow splicing at any point like sg_chain does, so I'd say it's less functional (not that I actually want anyone ever to do this, of course ...)
The final point is that sg_ring requires a two level traversal: ring list then scatterlist, whereas sg_chain only requires a single level traversal. I grant that we can abstract out the traversal into something that would make users think they're only doing a single level, but I don't see what the extra level really buys us.
The above analysis seems to suggest that sg_chain is simpler and has more functionality than sg_ring, unless I've missed anything?
The only thing missing from sg_chain perhaps is an accessor function that does the splicing, which I can easily construct if you want to try it out in virtio.
James
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