Messages in this thread |  | | Date | Wed, 28 Nov 2001 14:35:51 +0100 | From | Jens Axboe <> | Subject | Re: Block I/O Enchancements, 2.5.1-pre2 |
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On Tue, Nov 27 2001, Jeff V. Merkey wrote: > On Tue, Nov 27, 2001 at 05:04:46PM -0800, Linus Torvalds wrote: > > > > On Wed, 28 Nov 2001, Paul Mackerras wrote: > > > > > > Is there a description of the new block layer and its interface to > > > block device drivers somewhere? That would be helpful, since Ben > > > Herrenschmidt and I are going to have to convert several > > > powermac-specific drivers. > > > > Jens has something written up, which he sent to me as an introduction to > > the patch. I'll send that out unless he does a cleaned-up version, but I'd > > actually prefer for him to do the sending. Jens? > > > > Linus > > > > > Linus/Jens, > > I've just completed my review of submit_bio and the changes to > generic_make_request and I have some questions for whomever > can answer. > > 1. The changes made to submit_bh indicate I can now send long > chains of variable block size requests to the I/O layer similiar > to the capability of Windows 2000 and NetWare I/O subsystems.
Yes, you can build generically a single I/O unit that spans up to 256 pages. If you bypass the bio_alloc/bvec_alloc mechanism, the sky is the limit. Beware that a really big bio may need to be split up in the end for devices that can't handle them that big.
> 2. The elevator layer is merging these requests, and making a > single sweep request for contiguous sector runs.
Like always, yes.
> 3. In theory, I should be able to support page cache capability > for NWFS and possibly NTFS in Linux the way these wierd non-Unix > OS's work.
Maybe :-)
> 4. This interface may **NOT** support non-block aligned requests > across all the drivers. I also need to be able to submit a > request chain 512-2048-512-1024-4096 where the first IO requested > may by on a non-block aligned boundry. i.e. Device is configured > for 1024 byte blocks, I start the request as 512 @ LBA 1 -> 1024 @ LBA 2, > etc. The code looks like it will work.
As long as the smallest unit above is at least the size of the hardware sector on the target, it should be ok.
> I would love to test this wonderful code and will hopefully this evening, > however, all the SCSI drivers appear to be broken, as well as the > 3Ware. :-)
Well not all, but many. I only converted stuff I could personally test, basically, plus a bit more. Usually converting a SCSI driver is not a lot of work, please see the changes to sym/sym2 etc in the pre2 patch.
-- Jens Axboe
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