On Mon, Jul 16 2007, Martin K. Petersen wrote: > >>>>> "John" == John Stoffel <john@xxxxxxxxxxx> writes: > > John> Will this help out tape drive performance at all? I looked > John> through the patches quickly, esp the AIC7xxx stuff since that's > John> what I use, but nothing jumped out at me... > > Yes. Most modern tape drives want a block size of 1MB or higher. > With the old stack we'd be stuck at 512KB because the sg limitations > caused us to come just short of 1MB... Indeed. John, note that the driver changes aren't related to enabling some hardware feature. Drivers just need to be converted to use the sg walker helpers instead of doing it manually, then they'll also gain larger IO support. The SCSI drivers are currently being transitioned to that seperately, my patchset just contains patches for remaining drivers (which include non-SCSI ones as well). The hardware has to support a big number of segments of course, looking at aic7xxx it seems to be limited at 128. From the comment that looks like it can be increased though, see AHD_NSEG in drivers/scsi/aic7xxx/aic79xx_osm.h: /* * Number of SG segments we require. So long as the S/G segments for * a particular transaction are allocated in a physically contiguous * manner and are allocated below 4GB, the number of S/G segments is * unrestricted. */ #define AHD_NSEG 128 -- Jens Axboe - 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
