On Mon, May 01 2000, Stephen C. Tweedie wrote:
> > Is it necessary for the elevator sorting code to be hard-coded into the
> > kernel?
>
> Not necessary, but highly desirable.
It is highly desirable to have the sorting _hard coded_?
> > Elevator sorting offers little or no benefit to higher performance I./O
> > devices - An
> > extreme example would be RAID controllers that have on card memory that
> > can do
> > reordering more intelligently themselves.
>
> True, but only if the memory survives a reboot. However, even in
> these situations, the elevator serves a useful purpose --- it allows
> us to merge adjacent IO requests together in the queue, letting us
> reduce the number of hardware IOs we generate. That is still good
> for performance, as it reduces the CPU cost of the driver and may
> allow for significantly faster throughput between memory and the
> IO adapter.
But there's a difference between merging adjacent request,
which IMHO we should always do (for the reason you state) and forcing
a sort of a new request into the existing list.
-- * Jens Axboe <axboe@suse.de> * Linux CD/DVD-ROM, SuSE Labs * http://kernel.dk- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
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