On Fri, 2012-01-06 at 13:29 -0500, Chuck Lever wrote:
> On Jan 6, 2012, at 12:32 PM, Sasha Levin wrote:
>
> > Hi all,
> >
> > I've noticed a boot regression caused by commit 6829a048 ("NFS: Retry
> > mounting NFSROOT") which has increased boot time by 95 seconds.
> >
> > The scenario is as follows:
> > - A virtual guest running under the KVM tool.
> > - Guest is using kernel automatic IP DHCP configuration ("ip=dhcp").
> > - Guest is booting from a 9p device (which is not detected as block,
> > and gets mounted after NFS tries to do its mounts).
> > - No NFS server at all, no NFS parameters passed to the guest kernel.
> >
> > Under this scenario, theres an additional 95 second delay before NFS
> > fails and tries to boot using 9p:
> >
> > [...]
> > [ 6.505269] md: autorun ...
> > [ 6.506954] md: ... autorun DONE.
> > [ 101.522716] VFS: Unable to mount root fs via NFS, trying floppy.
> > [ 101.534499] VFS: Mounted root (9p filesystem) on device 0:18.
> > [...]
> >
> > This probably happens since the NFS server isn't configured, so the
> > bootserver is automatically assumed to be the DHCP server, and with the
> > commit above we won't simply fail immediately when the NFS code fails
> > connecting to it.
> >
> > I'm not quite sure about the correct solution for this. While I can
> > forcefully disable NFS, is it really the right solution? Should we be
> > retrying a NFS server even if one wasn't specifically set?
>
> What DHCP options are passed to the client? You can specify the "nfsrootdebug" boot command line option to explore this a little more.
This is what came out:
[ 5.220654] NFS: nfs mount opts='vers=2,udp,rsize=4096,wsize=4096,nolock,addr=0.0.0.0'
[ 5.226382] NFS: parsing nfs mount option 'vers=2'
[ 5.227707] NFS: parsing nfs mount option 'udp'
[ 5.228781] NFS: parsing nfs mount option 'rsize=4096'
[ 5.230307] NFS: parsing nfs mount option 'wsize=4096'
[ 5.231537] NFS: parsing nfs mount option 'nolock'
[ 5.232834] NFS: parsing nfs mount option 'addr=0.0.0.0'
[ 5.234069] NFS: mount program didn't pass remote address
> Typically ip= is used specifically with NFSROOT. You might review Documentation/filesystems/nfs/nfsroot.txt to see if some combination of boot command line options gives more desirable behavior.
Within nfsroot.txt, it says I should specify "root=/dev/nfs" so that
nfsroot would be used. Why do we try mounting nfsroot if I specifically
specify something else under "root="?
--
Sasha.
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