linux-kernel - Re: VFS scalability git tree

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Date:	Tue, 27 Jul 2010 21:09:58 +1000
From:	Nick Piggin <npiggin@...nel.dk>
To:	Nick Piggin <npiggin@...nel.dk>
Cc:	Dave Chinner <david@...morbit.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Frank Mayhar <fmayhar@...gle.com>,
	John Stultz <johnstul@...ibm.com>
Subject: Re: VFS scalability git tree

On Tue, Jul 27, 2010 at 05:05:39PM +1000, Nick Piggin wrote:
> On Fri, Jul 23, 2010 at 11:55:14PM +1000, Dave Chinner wrote:
> > On Fri, Jul 23, 2010 at 05:01:00AM +1000, Nick Piggin wrote:
> > > I'm pleased to announce I have a git tree up of my vfs scalability work.
> > > 
> > > git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin.git
> > > http://git.kernel.org/?p=linux/kernel/git/npiggin/linux-npiggin.git
> > > 
> > > Branch vfs-scale-working
> > 
> > With a production build (i.e. no lockdep, no xfs debug), I'll
> > run the same fs_mark parallel create/unlink workload to show
> > scalability as I ran here:
> > 
> > http://oss.sgi.com/archives/xfs/2010-05/msg00329.html
> 
> I've made a similar setup, 2s8c machine, but using 2GB ramdisk instead
> of a real disk (I don't have easy access to a good disk setup ATM, but
> I guess we're more interested in code above the block layer anyway).
> 
> Made an XFS on /dev/ram0 with 16 ags, 64MB log, otherwise same config as
> yours.

I also tried dbench on this setup. 20 runs of dbench -t20 8
(that is a 20 second run, 8 clients).

Numbers are throughput, higher is better:

          N           Min           Max        Median           Avg Stddev
vanilla  20       2219.19       2249.43       2230.43     2230.9915 7.2528893
scale    20       2428.21        2490.8       2437.86      2444.111 16.668256
Difference at 95.0% confidence
        213.119 +/- 8.22695
        9.55268% +/- 0.368757%
        (Student's t, pooled s = 12.8537)

vfs-scale is 9.5% or 210MB/s faster than vanilla.

Like fs_mark, dbench has creat/unlink activity, so I hope rcu-inodes
should not be such a problem in practice. In my creat/unlink benchmark,
it is creating and destroying one inode repeatedly, which is the
absolute worst case for rcu-inodes. Wheras in most real workloads
would be creating and destroying many inodes, which is not such a dis
advantage for rcu-inodes.

Incidentally, XFS was by far the fastest "real" filesystem I tested on
this workload. ext4 was around 1700MB/s (ext2 was around 3100MB/s and
ramfs is 3350MB/s).

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