Messages in this thread | | | Date | Thu, 6 Nov 2003 18:14:09 +0100 | From | Jens Axboe <> | Subject | Re: [ANNOUNCE] QLogic qla2xxx driver update available (v8.00.00b6). |
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On Thu, Nov 06 2003, Andrew Vasquez wrote: > Jens, > > > > o Given the ISPs inability to handle data segments that cross > > > 32-bit page boundaries, and the overhead in defensive logic > > > within the driver to prevent these cases (compare the 6.x > > > code to the 8.x code and you will see what I mean), by > > > disabling clustering we guarantee that a single SG element > > > never crosses a 4GB boundary. > > > > That is not, however. Linux will never give you a segment crossing a > > 4GB boundary, exactly because most hardware cannot handle this. > > > > > Now, in 2.6 there are some significant changes. For one, with the > > > block layer rewrite and the ability to limit segment boundaries of a > > > block queue request with the blk_queue_segment_boundary() call, a LLDD > > > need not concern itself with any defensive fast-path logic to handle > > > the 4GB cross. > > > > Ditto 2.4. See BH_PHYS_4G(). > > > > Yes, but if I recall, these checks did not enter until late in the 2.4 > branch. The original (engineering) intent of the 6.x series branch > was to support all 2.4 kernels, though we are slowly (formally) moving > away from the restrictions.
They were there at the same time as Linux supported > 1GB IO at all. So that is incorrect, it's been there all along.
> > > So, we're left with the benefits of the overhead of this merge > > > process done by the block layer. I'm certainly receptive to the > > > notion of reexamining the use of clustering given some solid data > > > points showing an (significant -- this is subjective) increase in > > > performance and/or a resounding 'yeah, enable it!' from those in > > > the block-layer 'know.' > > > > In 2.6 clustering comes for free, so it would be silly not to enable > > it. > > > > Thanks for the clarification, I'll add the parameter back into the > template for the 8.x series driver.
Cool, thanks.
-- Jens Axboe
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