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

[Nick Piggin <piggin@cyberone.com.au>]

Jeremy Higdon wrote:

>| 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.
>
>

Nice - so if you had enough IO capacity to saturate the CPUs it
might come close to a 4x improvement - and this sounds like one
of your baby systems?

I wonder why nobody's complained about this before?