On Mon, 31 Dec 2007, James Bottomley wrote: > 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). ... > diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c > index 7c9593b..39c03f9 100644 > --- a/drivers/usb/storage/scsiglue.c > +++ b/drivers/usb/storage/scsiglue.c > @@ -82,6 +82,12 @@ static int slave_alloc (struct scsi_device *sdev) > sdev->inquiry_len = 36; > > /* > + * Update the dma alignment (minimum alignment requirements for > + * start and end of DMA transfers) to be a sector > + */ > + blk_queue_update_dma_alignment(sdev->request_queue, 511); > + > + /* > * The UFI spec treates the Peripheral Qualifier bits in an > * INQUIRY result as reserved and requires devices to set them > * to 0. However the SCSI spec requires these bits to be set It would be better to move the existing code from the start of slave_configure() up into slave_alloc(). Otherwise it's fine. Alan Stern - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
