> -----Original Message----- > From: James Bottomley [mailto:James.Bottomley@xxxxxxx] > Sent: Wednesday, February 10, 2010 3:59 PM > To: scameron@xxxxxxxxxxxxxxxxxx > Cc: linux-scsi@xxxxxxxxxxxxxxx; Miller, Mike (OS Dev) > Subject: Re: 16 commands per lun limitation bug? > > On Wed, 2010-02-10 at 14:19 -0600, scameron@xxxxxxxxxxxxxxxxxx wrote: > > We have seen the amount of commands per lun that are sent > to low level > > scsi driver limited to 16 commands per lun, (seemingly > artificially, > > well below our can_queue and cmd_per_lun limits of 1020) > > > > 2.6.29 does not exhibit this bad behavior. > > 2.6.30, 2.6.31, 2.6.32 (2.6.32.1 through 2.6.32.8) do > exhibit this bad > > behavior > > 2.6.31-rc1 does not exhibit this bad behavior > > I can't think of any reason for this. Best guess at the fix > would be the new queue full ramp up ramp down code, but no > clue as to what the problem is ... no other drivers seem to > have noticed the performance problems this would likely cause > ... and 2.6.32 is becoming the standard enterprise kernel. > James, I'm not sure there's much hardware out there that's capable of queuing up so many commands without choking the disks. I _think_ in most cases if you queue up say 64 commands on a single scsi disk that's just too much. But with Smart Array we can queue up to 1024 commands (on most controllers) and those are then distributed across all the drives in the array(s). IOW, we're thinking not many people would have noticed such a change. Hope this makes sense. -- mikem -- 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
