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.
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.
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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