Date: Thu, 9 Feb 2012 08:48:13 -0600
From: Malahal Naineni <malahal@us.ibm.com>
To: "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: NFS Mount Option 'nofsc'
Message-ID: <20120209144812.GA15569@us.ibm.com>
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Harshula [harshula@redhat.com] wrote:
> Hi Trond,
> 
> Thanks for the reply. Could you please elaborate on the subtleties
> involved that require an application to be rewritten if forcedirectio
> mount option was available?
> 
> On Thu, 2012-02-09 at 04:12 +0000, Myklebust, Trond wrote:
> > On Thu, 2012-02-09 at 14:56 +1100, Harshula wrote:
> > >
> > > The "sync" option, depending on the NFS server, may impact the NFS
> > > server's performance when serving many NFS clients. But still worth a
> > > try.
> > 
> > What on earth makes you think that directio would be any different?
> 
> Like I said, sync is still worth a try. I will do O_DIRECT Vs sync mount
> option runs and see what the numbers look like. A while back the numbers
> for cached Vs direct small random writes showed as the number of threads
> increased the cached performance fell well below direct performance. In
> this case I'll be looking at large streaming writes, so completely
> different scenario, but I'd like to verify the numbers first.

directio and sync behavior should be same on server side, but it would
be a different story on the client though. The above behavior you
described is expected on the client.

Thanks, Malahal.