Re: [PATCH] per-backing dev unplugging #2

[Jeremy Higdon <jeremy@sgi.com>]

| Hi,
| 
| Final version, unless something stupid pops up. Changes:
| 
| - Adapt to 2.6.4-mm1
| - Cleaned up the dm bits, much nicer with the lockless unplugging
|   (thanks Joe)
| - md and loop unplugging, stacked devices should unplug their targets.
|   Otherwise they'll end up waiting for the unplug timer, which sucks.
| - XFS fixed up, I hope. XFS folks still encouraged to look at this,
|   looks better this time around though (and works, I tested).
| - blk_run_* inlined in blkdev.h
| 
| Against 2.6.4-mm1 (note you need other attached patch to boot it).

I got a chance to try this.

It makes a huge improvement.

Prior to the last per-cpu patch, I was getting about 75000 to 80000
IOPS at 100% cpu usage.

With the per-cpu patch, that went up to 110000 IOPS at 100% CPU.

With this patch, I'm seeing 200000 IOPS at about 65% CPU usage.

So it makes a tremendous improvement in I/O scalability, dramatically
improving performance in small size I/O, high I/O count workloads.

My tests were on an 8 CPU x 1300 MHz Altix with 64 disks.

jeremy