Re: Why is NCQ enabled by default by libata? (2.6.20)

Jeff Garzik
2007-03-27T05:59:24Z

Justin Piszcz wrote:
> Without NCQ, performance is MUCH better on almost every operation, with
> the exception of 2-3 items.

Variables to take into account:

* the drive (NCQ performance wildly varies)
* the IO scheduler
* the filesystem (if not measuring direct to blkdev)
* application workload (or in your case, benchmark tool)
* in particular, the threaded-ness of the apps

For the overwhelming majority of combinations, NCQ should not /hurt/
performance.

For the majority of combinations, NCQ helps (though it may not be often
that you use more than 4-8 tags).

In some cases, NCQ firmware may be broken. There is a Maxtor firmware
id, and some Hitachi ids that people are leaning towards recommending be
added to the libata 'horkage' list.

Jeff