From: Olaf Kirch <okir@suse.de>
Subject: Re: RE: Chuck's iostat patch
Date: Tue, 9 Mar 2004 15:15:02 +0100
Sender: nfs-admin@lists.sourceforge.net
Message-ID: <20040309141502.GB14419@suse.de>
References: <482A3FA0050D21419C269D13989C611302B07BB9@lavender-fe.eng.netapp.com>
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Cc: Jeremy McNicoll <jeremy@mcnicoll.ca>, nfs@lists.sourceforge.net
To: "Lever, Charles" <Charles.Lever@netapp.com>
In-Reply-To: <482A3FA0050D21419C269D13989C611302B07BB9@lavender-fe.eng.netapp.com>
Errors-To: nfs-admin@lists.sourceforge.net

On Tue, Mar 09, 2004 at 05:58:46AM -0800, Lever, Charles wrote:
> i don't have a 2.6 version nor have i started any modification of
> iostat or sar.  i simply wanted to get agreement on APIs and exactly
> what metrics we are interested in providing.  as such this is only
> a prototype.  there are some ugly things that will change in the
> final version (nfs_count_this_op, i believe, is going away).

That is good. I very much prefer doing all the iostat stuff
inside the RPC layer, without having to modify NFS very much
(except for a single call to enable iostat collection for the
rpc_clnt)

> # optype   op count                bytes    retrans     errors

I would like to see separate in/out byte counts.

> there are a few problems with this solution.  one is that zeroing
> these counters is not atomic.  another is that umount is racy and
> can leave these data structures in a not so friendly state that
> could result in an oops.

I've addressed that by putting the rpc_clnt pointer into the proc dir
entry, and make it bump the refcount when the file is opened and call
rpc_release_client() when the file is closed.

> and i think we all agree that using
> seq_file is a much better way to export these metrics to user space.
> in the final version we will use sysfs instead of /proc.  it's
> not clear how to name the stat files uniquely -- today i'm using
> minor numbers, which is a hack.

It's a reasonable compromise. You can even use a simple monotonic counter
or the %p representation of the rpc_clnt pointer as the file name -
it should be up to iostat/sar to display something reasonable to the
user. You can help it by making nfs_show_options() give a hint which
iostat file corresponds to which mount.

> for use in the stat files.  in 2.6 we have superblock sharing, and
> i'm not sure what exactly that will mean for the "per-mountpoint"
> nature of this implementation.

Well, that is not an issue in this case I think. Only super blocks
with the same file handle get shared.

Olaf
-- 
Olaf Kirch     |  Stop wasting entropy - start using predictable
okir@suse.de   |  tempfile names today!
---------------+ 


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