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

[Jens Axboe <axboe@suse.de>]

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