Bio pool & scsi scatter gather pool usage
Andrew Morton <[email protected]> wrote:
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Quoted 3 lines
Right now,
BIO_MAX_SECTORSis only 64k, and IDE can take twice that. I'm not sure what the largest request size is for SCSI - certainly 128k.
Scatter gather lists in the scsi subsystem have a max length of 255. The actual maximum size is dictated by the HBA driver (sg_tablesize). The HBA driver can further throttle the size of a single transfer with max_sectors.
Experiments with raw IO (both in 2.4 and 2.5) indicate that pages are not contiguous when the scatter gather list is built. On i386 this limits the maximum transfer size of a single scsi command to just less than 1 MB.
Doug Gilbert