Re: high load, no bottleneck

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Tue, Sep 24, 2013 at 04:01:36PM +0100, David Brownlee wrote:
> crap, apologies for the non checked return address.
> 
> In the interest of trying to make a relevant reply - doesn't nfs3
> support differing COMMIT sync levels which could be leveraged for
> this? (assuming your server is stable :)

There's something else going on here, I think.

If I understand the problem correctly, we have many concurrent streams of
client I/O each of which includes a large number of fsync requests.

It should be possible to gather those requests and commit many of them
at once to disk with a single cache flush operation, rather than issuing
a cache flush for each one.  This is not unlike the problem with nfs3 in
general, that many clients at once may issue WRITE RPCs followed by COMMIT
RPCs, and the optimal behavior is to gather the COMMITS, service many at
a time, then respond to them all -- but our NFS server code is not great
at this.

Nonetheless, it should be possible!

Thor