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Re: XFS: performance

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: XFS: performance
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 30 Nov 2010 15:29:13 +1100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4CF33D0F.6080404@xxxxxxxxxxxxxxxxx>
References: <AANLkTi=u8dX0ehPN3Rv3FQ+84htY3AYEv0eboGgC7_qi@xxxxxxxxxxxxxx> <20101129001112.GA28672@dastard> <AANLkTikom6jpkuZquTfinGpaqz4Gp0y8niYN7yWQgmzj@xxxxxxxxxxxxxx> <20101129015937.GB28672@dastard> <AANLkTikw086Z_66cz_U-EdFQx14TXP6XmiG-KyLN4BLo@xxxxxxxxxxxxxx> <AANLkTi=-y0v4MzyU+qWPmvazouDu0N3gqSvVTU1z4Gke@xxxxxxxxxxxxxx> <4CF33D0F.6080404@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Sun, Nov 28, 2010 at 11:41:35PM -0600, Stan Hoeppner wrote:
> Yclept Nemo put forth on 11/28/2010 9:57 PM:
> > You mention an eight-core machine (8c?). Since I operate a dual-core
> > system, would it make sense to increase my AG count slightly, to five
> > or six?
> 
> Dave didn't mention the disk configuration of his "workstation".  I'm
> guessing he's got a local RAID setup with 8-16 drives.

2 SSDs in RAID0.

> AG count has a
> direct relationship to the storage hardware, not the number of CPUs
> (cores) in the system.

Actually, I used 16 AGs because it's twice the number of CPU cores
and I want to make sure that CPU parallel workloads (e.g. make -j 8)
don't serialise on AG locks during allocation. IOWs, I laid it out
that way precisely because of the number of CPUs in the system...

And to point out the not-so-obvious, this is the _default layout_
that mkfs.xfs in the debian squeeze installer came up with. IOWs,
mkfs.xfs did exactly what I wanted without me having to tweak
_anything_.

> If you have a 24 core system (2x Magny Cours)
> and a single disk, creating an FS with 24 AGs will give you nothing, and
> may actually impede performance due to all the extra head seeking across
> those 24 AGs.

In that case, you are right. Single spindle SRDs go backwards in
performance pretty quickly once you go over 4 AGs...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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