Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]

[Andrea Arcangeli]

On Mon, Feb 10, 2003 at 03:21:01AM -0800, Andrew Morton wrote:
> Andrea Arcangeli <[e-mail]> wrote:
> >
> > On Mon, Feb 10, 2003 at 09:40:34PM +1100, Nick Piggin wrote:
> > > I don't know too much about SCSI stuff, but if driver / wire / device
> > > overheads were that much higher at 128K compared to 512K I would
> > > think something is broken or maybe optimised badly.
> > 
> > I guess it's also a matter of the way the harddisk can serve the I/O if
> > it sees it all at the same time, not only the cpu/bus protocol after all
> > minor overhead.  Most certainly it's not a software mistake in linux
> > that the big commands runs that much faster. Again go check the numbers
> > in bigbox.html between my tree, 2.4 and 2.5 in bonnie read sequential,
> > to see the difference between 128k commands and 512k commands with
> > reads, these are facts.  (and no writes and no seeks here)
> > 
> 
> I thought scsi in 2.5 was doing 512k I/O's at present???
> 
> Doesn't Randy attribute the differences there to an updated
> qlogic driver?   (Or was the update to allow 512k I/O's? ;))

The special case of the qlogic that Randy is using does 256k commands
with the new driver.

Andrea