Messages in this thread | | | Date | Wed, 14 May 2003 09:54:07 +0200 | From | Jens Axboe <> | Subject | Re: drivers/scsi/aic7xxx/aic7xxx_osm.c: warning is error |
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On Wed, May 14 2003, Mike Anderson wrote: > Justin T. Gibbs [gibbs@scsiguy.com] wrote: > > Comments have indicated since the 2.4.X days that Linux will never allocate > > segments that cross a 4GB boundary. If this is truely enforced, then this > > code can just be removed. It was only added out of paranoia (hence the > > printf) while adding high address support to the driver. > > Jens can give the more complete answer on enforcement, and also correct > any mis-statements I made.
This property can be toggled with blk_queue_segment_boundary, and we do default to setting a 4GB boundary mask. So you can be sure that a request will never straddle a 4GB boundary.
> Base on the queue values below the aic7xxx driver should see the > following characteristics on IO. The IO should be for no more than 8k > made up of no more than 128 sg entries with no segment crossing the > seg_boundary_mask.
I suppose you mean for no more than 8k sectors, ie 4MiB of data.
> Adaptec AIC7xxx driver version: 6.2.33 > scsi_alloc_queue: queue for aic7xxx > bounce_pfn: 0xfffff > bounce_gfp: 0x10 (GFP_NOIO) > queue_flags: 0x1 (QUEUE_FLAG_QUEUED) > max_sectors: 0x2000 (8192) > max_phys_segments: 0x80 (128) > max_hw_segments: 0x80 (128) > hardsect_size: 0x200 (512) > max_segment_size: 0x10000 (65536) > seg_boundary_mask: 0xffffffff
that is the key here.
> dma_alignment: 0x1ff (511)
So to recap, aic7xxx will never see a request that exceeds one of the above values. Total request size will always be equal to or below 4MiB, less than or equal to 128 segments, and will never cross a 4GB memory boundary. Memory above pfn 0xfffff (4GB) will be bounced, but this could be because that's just the amount of memory the box has you dumped this info from.
-- Jens Axboe
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