Messages in this thread | | | Date | Fri, 19 Apr 2002 13:15:13 -0500 (CDT) | From | Oliver Xymoron <> | Subject | Re: Bio pool & scsi scatter gather pool usage |
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On Thu, 18 Apr 2002, Andrew Morton wrote:
> Alan Cox wrote: > > > > > Perhaps, but calls are expensive. Repeated calls down stacked block > > > devices will add up. In only the most unusually cases will there > > > > You don't need to repeatedly query. At bind time you can compute the > > limit for any device heirarchy and be done with it. > > > > S'pose so. The ideal request size is variable, based > on the alignment. So for exampe if the start block is > halfway into a stripe, the ideal BIO size is half a stripe. > > But that's a pretty simple table to generate once-off, > as you say.
Perhaps we can return request size _and_ stripe alignment at bind time. Then we can do the right thing for RAID/LVM/etc in a pretty straightforward manner. LVMs of RAIDs can return an GCD(LVM stripe, RAID stripe) and non-striped devices can return 0 to indicate no restrictions.
-- "Love the dolphins," she advised him. "Write by W.A.S.T.E.."
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