Re: [PATCH] 2.4.x write barriers (updated for ext3)

Stephen C. Tweedie
2002-03-04T19:56:30Z

Hi,

On Mon, Mar 04, 2002 at 12:28:19PM -0600, James Bottomley wrote:

> There is one remaining curiosity I have, at least about the benchmarks: Since
> the linux elevator and tag queueing perform essentially similar function
> (except that the disk itself has a better notion of ordering because it knows
> its own geometry). Might we get better performance by reducing the number of
> tags we allow the device to use, thus forcing the writes to remain longer in
> the linux elevator?

Possibly, but my gut feeling says no and so do any benchmarks I've
seen regarding queue depths on adaptec controllers (not that I've seen
many). For relatively-closeby IOs, the disk will always have a better
idea of how to optimise a number of IOs than the Linux elevator can
have, especially if we have multiple IOs spanning multiple heads
within a single cylinder.

--Stephen