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On Sun, Mar 28, 2004 at 06:36:23PM +0100, Jamie Lokier wrote: > > This is what I mean: turn off write cacheing, and performance on PATA > drops because of the serialisation and lost inter-command time. Since you have to write the sectors in order (well, you don't have to, but the drives all do this), you lose a rev between each write when you don't queue commands or have write cacheing. > With TCQ-on-write, you can turn off write cacheing and in theory > performance doesn't have to drop, is that right? Correct. I have proven this to my satisfaction. Regarding request sizes, the main benefit to very large (> 1MB) request sizes to disk drives is elimination of the lost revolution when write cacheing is disabled and you can't queue back-to- back writes. For hardware RAID, they frequently need 4MB or more to hit peak performance. I agree that we don't want a host driver to arbitrarily limit I/O size, because it's difficult to predict what may be connected to it. It may be necessary due to deficiencies elsewhere, but not desired. jeremy - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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