xfs
[Top] [All Lists]

Re: 12x performance drop on md/linux+sw raid1 due to barriers [xfs]

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: 12x performance drop on md/linux+sw raid1 due to barriers [xfs]
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 15 Dec 2008 10:36:17 +1100
Cc: Martin Steigerwald <Martin@xxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx, linux-raid@xxxxxxxxxxxxxxx, Alan Piszcz <ap@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <4943F37B.8080405@xxxxxxxxxxx>
Mail-followup-to: Eric Sandeen <sandeen@xxxxxxxxxxx>, Martin Steigerwald <Martin@xxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx, linux-raid@xxxxxxxxxxxxxxx, Alan Piszcz <ap@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
References: <alpine.DEB.1.10.0812060928030.14215@xxxxxxxxxxxxxxxx> <493A9BE7.3090001@xxxxxxxxxxx> <alpine.DEB.1.10.0812130724340.18746@xxxxxxxxxxxxxxxx> <200812131826.25280.Martin@xxxxxxxxxxxx> <4943F37B.8080405@xxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Sat, Dec 13, 2008 at 11:40:11AM -0600, Eric Sandeen wrote:
> Martin Steigerwald wrote:
> 
> > At the moment it appears to me that disabling write cache may often give 
> > more performance than using barriers. And this doesn't match my 
> > expectation of write barriers as a feature that enhances performance. 
> 
> Why do you have that expectation?  I've never seen barriers advertised
> as enhancing performance.  :)
> 
> I do wonder why barriers on, write cache off is so slow; I'd have
> thought the barriers were a no-op.  Maybe I'm missing something.

Barriers still enforce ordering in this case, so it affects the
elevator algorithm....

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

<Prev in Thread] Current Thread [Next in Thread>