blkdev speedup

[Andrea Arcangeli <andrea@suse.de>]

On Wed, Jan 16, 2002 at 11:44:37PM +0100, Chris Chabot wrote:
> 
> > Test hardware:
> > 4 way Dell, 4 GB physical RAM, SCSI/RAID subsystem,
> > DB runs on FS.
> 
> Can we first make sure that the other factors dont plat a rol in this 
> benchmark? I have a couple (14+) Dell servers here, and i know for a 
> fact that most of their RAID systems are heavely borked in the 
> performance department.
> 
> All kernels upto 2.4.1x performed horibly, and all kernels after 2.4.16 
> or so perform horibly again! Somewhere inbetween some magic seemed to 
> happen in the block layer / elevator code / etc, that caused performance 
> to increase upto 100% on the Dell PERC adapters. (started @ the first 
> release of the AA VM). However after a few small releases, the 

if you're using the blkdev directly, then please try to mount the blkdev
with a 4k filesystem before making your benchmark, that should give you
the magic performance back. 2.4.10 intentionally were defaulting to 4k
I/O, this is probably what made the difference for you.

Andrea