Messages in this thread | | | Date | Mon, 6 May 2002 19:50:37 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] IDE TCQ for 2.4.19-pre8 |
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On Mon, May 06 2002, Erik Andersen wrote: > On Mon May 06, 2002 at 03:45:35PM +0200, Jens Axboe wrote: > > People who were (rightfully so) afraid to test 2.5 can now play with ide > > tagged queueing in 2.4. Works great here. > > What sort of behavior changes should I expect to see? Faster? > Less CPU utilization? Are there limited set of controllers and/
I find CPU utilization to be about the same, sometimes a bit more with TCQ (seems to be due to excessive spinning waiting for BUSY_STAT to clear after outputting a command (WIN_READMA_QUEUED etc). This will be the subject of some more investigation.
Streamed reads or writes of 512 byte units is slower with TCQ, by as much as 20% or so. Approaching 4kb transfers and TCQ catches up, 4kb and up they are equally fast.
Random reads are somewhat faster, this is the case that we expect to be faster. Random writes run at the same speed, but that's merely due to write caching in the non-tcq case. Random access reads show up to 30% improvement.
> or drives on which this works?
See the configure help entry for known good drives. All controllers should work, I've tested:
- PIIX4 (various revisions) - Promise pdc202xx - AMD 768
others should work as well.
-- Jens Axboe
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