Messages in this thread | | | Date | Wed, 14 May 2003 08:56:53 -0700 | From | Mike Anderson <> | Subject | Re: drivers/scsi/aic7xxx/aic7xxx_osm.c: warning is error |
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Jens Axboe [axboe@suse.de] wrote: > 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. >
Yes, late night typing (my brain went to sleep before my fingers).
> > 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. >
The system I dumped the info from only has 256MB. SCSI calls blk_queue_bounce_limit with the return value of scsi_calculate_bounce_limit which takes the dma_mask set by the adapter. Some adapters set this value based the adapters capabilities and CONFIG_HIGHMEM64G, but the aic7xxx also checks the memsize.
My config on this system also has (CONFIG_HIGHMEM64G, CONFIG_HIGHMEM, and CONFIG_X86_PAE) set.
-andmike -- Michael Anderson andmike@us.ibm.com
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