linux-kernel - Re: [PATCH 00/19] Hardware Accelerated MD RAID5: Introduction

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Date:	Wed, 13 Sep 2006 12:17:55 -0700
From:	"Dan Williams" <dan.j.williams@...il.com>
To:	"Jakob Oestergaard" <jakob@...hought.net>,
	"Dan Williams" <dan.j.williams@...el.com>,
	NeilBrown <neilb@...e.de>, linux-raid@...r.kernel.org,
	akpm@...l.org, linux-kernel@...r.kernel.org,
	christopher.leech@...el.com
Subject: Re: [PATCH 00/19] Hardware Accelerated MD RAID5: Introduction

On 9/13/06, Jakob Oestergaard <jakob@...hought.net> wrote:
> On Mon, Sep 11, 2006 at 04:00:32PM -0700, Dan Williams wrote:
> > Neil,
> >
> ...
> >
> > Concerning the context switching performance concerns raised at the
> > previous release, I have observed the following.  For the hardware
> > accelerated case it appears that performance is always better with the
> > work queue than without since it allows multiple stripes to be operated
> > on simultaneously.  I expect the same for an SMP platform, but so far my
> > testing has been limited to IOPs.  For a single-processor
> > non-accelerated configuration I have not observed performance
> > degradation with work queue support enabled, but in the Kconfig option
> > help text I recommend disabling it (CONFIG_MD_RAID456_WORKQUEUE).
>
> Out of curiosity; how does accelerated compare to non-accelerated?

One quick example:
4-disk SATA array rebuild on iop321 without acceleration - 'top'
reports md0_resync and md0_raid5 dueling for the CPU each at ~50%
utilization.

With acceleration - 'top' reports md0_resync cpu utilization at ~90%
with the rest split between md0_raid5 and md0_raid5_ops.

The sync speed reported by /proc/mdstat is ~40% higher in the accelerated case.

That being said, array resync is a special case, so your mileage may
vary with other applications.

I will put together some data from bonnie++, iozone, maybe contest,
and post it on SourceForge.

>  / jakob

Dan
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