Re: NCQ performance (was Re: [rfc][patch] remove racy sync_page?)

Jens Axboe
2006-06-01T18:02:19Z

On Thu, Jun 01 2006, Jens Axboe wrote:
> On Thu, Jun 01 2006, Avi Kivity wrote:
> > Jens Axboe wrote:
> > >
> > >Ok, I decided to rerun a simple random read work load (with fio), using
> > >depths 1 and 32. The test is simple - it does random reads all over the
> > >drive size with 4kb block sizes. The reads are O_DIRECT. The test
> > >pattern was set to repeatable, so it's going through the same workload.
> > >The test spans the first 32G of the drive and runtime is capped at 20
> > >seconds.
> > >
> >
> > Did you modify the iodepth given to the test program, or to the drive?
> > If the former, then some of the performance increase came from the Linux
> > elevator.
> >
> > Ideally exactly the same test would be run with the just the drive
> > parameters changed.
>
> Just from the program. Since the software depth matched the software
> depth, I'd be surprised if it made much of a difference here. I can
> rerun the same test tomorrow with the drive depth modified the and
> software depth fixed at 32. Then the io scheduler can at least help the
> drive without NCQ out somewhat.

Same test, but with iodepth=48 for both ncq depth 1 and ncq depth 31.
This gives the io scheduler something to work with for both cases.

sda: Maxtor 7B300S0
sdb: Maxtor 7L320S0
sdc: SAMSUNG HD160JJ
sdd: HDS725050KLA360 (Hitachi 500GB drive)

drive depth KiB/sec diff diff 1/1
----------------------------------------------------------------
sda 1/1 397
sda 1 513 +29%
sda 31 673 +31+ +69%

sdb 1/1 397
sdb 1 535 +35%
sdb 31 741 +38% +87%

sdc 1/1 372
sdc 1 449 +21%
sdc 31 507 +13% +36%

sdd 1/1 489
sdd 1 650 +33%
sdd 31 941 +45% +92%

Conclusions: the io scheduler helps, NCQ help - both combined helps a
lot. The Samsung firmware looks bad. Additional requests in io scheduler
when using NCQ doesn't help, except for the new firmware Maxtor.
Suspect. NCQ still helps a lot, > 30% for all drives except the Samsung.

--
Jens Axboe