[Lustre-devel] replacing Lustre pings with LNet Peer Health

[Isaac Huang <isaac_huang@xyratex.com>]

On Thu, May 12, 2011 at 09:57:41AM -0500, Nic Henke wrote:
> ......
> Issues...
> 
> - lacks "proof" that peer nodes ptlrpc queues are moving forward,
> but not really sure that is all that important in terms of pinger
> evictions.
> 
> - LNet peer health is a bit "weird" in that it requires an upper
> layer sending a packet to trigger a node moving back to 'up'. We
> would need to address this for proper LNet peer health as it is.

The idea was that if upper layer has no interest sending him a message
LNet is not bothered whether he's become "up" again. But care must be
taken such that a message from upper layer must not be dropped if it's
destined to a peer that appears "dead" but LNet isn't so sure of it,
i.e. that death news was too old and we haven't tried to get some
update yet. All is so that unnecessary pings could be cut off.

This is also why router pinger can't be replaced by Peer Health -
there'd be no more message to a dead router without router pinger
being active.

As others have pointed out, Peer Health is not end-to-end.

Thanks,
Isaac
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