blkdev speedup

Andrea Arcangeli
2002-01-17T14:14:11Z

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