Messages in this thread | | | Date | Thu, 29 Mar 2007 14:51:34 -0400 | From | Jeff Garzik <> | Subject | Re: Why is NCQ enabled by default by libata? (2.6.20) |
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Phillip Susi wrote: > Jeff Garzik wrote: >> NCQ provides for a more asynchronous flow. It helps greatly with >> reads (of which most are, by nature, synchronous at the app level) >> from multiple threads or apps. It helps with writes, even with write >> cache on, by allowing multiple commands to be submitted and/or retired >> at the same time. > > But when writing, what is the difference between queuing multiple tagged > writes, and sending down multiple untagged cached writes that complete > immediately and actually hit the disk later? Either way the host keeps > sending writes to the disk until it's buffers are full, and the disk is > constantly trying to commit those buffers to the media in the most > optimal order.
Less overhead to starting commands, and all the other benefits of making operations fully async.
Jeff
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