On Wed, Apr 18, 2007 at 07:32:03AM -0400, James Bottomley wrote: > I don't think so: simply increasing the phys segments has no effect on a > fully fragmented sg list if the hw segments doesn't go up to match it. Yes, of course. It is then up to each scsi lld to increase max_hw_segments accordingly. Increasing the phys segments seemed to me to be the first logical step. FYI, I tested the patch with lpfc and LPFC_SG_SEG_CNT set to 1024. > Since changing the hw segments necessitates driver work, I'd really like > to see justification in terms of throughput figures versus transfer size > rather than vague assertions that bigger is better. Sure. A full survey (done with sgp_dd) of DDN S2A9550 was posted on the lustre-discuss mailing list in January: https://mail.clusterfs.com/pipermail/lustre-discuss/2007-January/002795.html http://mail.clusterfs.com/pipermail/lustre-discuss/attachments/20070118/8d6a4e79/9500-sgp_dd-0001.xls For instance, here are the results obtained with 32 threads / 32 regions and write-back caching disabled: Transfer size Throughput (Write) Throughput (Read) 512KB 36MB/s 108MB/s 1MB 60MB/s 108MB/s 2MB 96MB/s 165MB/s 4MB 144MB/s 228MB/s Johann - 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
