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[SCSI] relax scsi dma alignment

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This patch relaxes the default SCSI DMA alignment from 512 bytes to 4
bytes.  I remember from previous discussions that usb and firewire have
sector size alignment requirements, so I upped their alignments in the
respective slave allocs.

The reason for doing this is so that we don't get such a huge amount of
copy overhead in bio_copy_user() for udev.  (basically all inquiries it
issues can now be directly mapped).

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
This commit is contained in:
James Bottomley
2008-01-01 10:00:10 -06:00
parent 11c3e689f1
commit 465ff3185e
5 changed files with 34 additions and 11 deletions
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8
drivers/scsi/scsi_lib.c
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@ -1668,6 +1668,14 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
if (!shost->use_clustering)
clear_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
/*
* set a reasonable default alignment on word boundaries: the
* host and device may alter it using
* blk_queue_update_dma_alignment() later.
*/
blk_queue_dma_alignment(q, 0x03);
return q;
}
EXPORT_SYMBOL(__scsi_alloc_queue);