On Fri, 2006-02-03 at 10:34 +0100, Hannes Reinecke wrote: > Can someone explain to my how having a queue depth of '2' in the non-TCQ > case can be correct? > If not, please apply the following patch. Oh, and aic7xxx suffers from > the same problem, naturally. Yes, the driver is supposed to be counting both the tagged and untagged commands outstanding and return SCSI_MLQUEUE_DEVICE_BUSY if the mid-layer tries to queue over that. The premise of setting this to 2 is that we always have one command in progress and one completely prepared ready to fire as soon as the in-progress one returns. Jens has postulated that this is no-longer necessary; we could simply reduce the queue depth to 1 for the non-TCQ case. What this would do is transfer the setup work from the sending process to the block softirq, so it might increase latency in the non-TCQ case ... but no-one knows for sure. James - : 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
