Re: [PATCH v1 00/12] netoops support

Randy Dunlap
2010-11-03T18:51:58Z

On Wed, 3 Nov 2010 11:16:34 -0700 Greg KH wrote:

> On Tue, Nov 02, 2010 at 08:37:42PM -0700, Mike Waychison wrote:
> > On Tue, Nov 2, 2010 at 7:34 PM, Greg KH <greg@kroah.com> wrote:
> > > On Tue, Nov 02, 2010 at 06:29:25PM -0700, Mike Waychison wrote:
> > >> This patchset applies to v2.6.36.
> > >>
> > >> The following series implements support for 'netoops', a simple driver that
> > >> will deliver kmsg logs together with machine specifics over the network.
> > >
> > > We already have the ability to send oopses over the network today,
> > > through the network consolst stuff. What does this patch set do that is
> > > different from our existing stuff that warrants such a big change?
> > >
> >
> > Hi Greg,
> >
> > I am a little familiar with the netconsole suppport. I should have
> > added a comparison to the cover email :(
> >
> > We never adopted netconsole for a couple different reasons. The
> > reasons have slightly changed over the years, but even today we find
> > that it isn't a substitute for netoops' semantics.
>
> Ah, but it sounds like it would be better to fix up netoops to handle
> your needs.
>
> > With the number of machines we have, streaming large amounts of
> > consoles within the data center can really add up. This gets worse
> > when you take into account how reliant we are on kernel logging like
> > OOM conditions (which are very regular and very verbose). Events in
> > the data center (such as application growth) tend to be temporally
> > correlated, which causes large bursts of logging when we are OOM. We
> > aren't so interested in this kernel verbosity from a global collection
> > standpoint though, and haven't been keen on the amount of extra
> > un-regulated UDP traffic it would generate. We are however interested
> > in kernel oopses though (which occur far less often).
>
> Understood, I'm sure that a change to allow this to the existing netoops
> code would be appreciated by many.
>
> > In terms of the data received, we've really benefited by having
> > structured data in the payload.
>
> I bet the whole world would benefit by having the oops messages in a
> more "structured" manner. We have done changes in the past to provide
> this type of thing in a "more parsable" manner, to help stuff like
> kerneloops.org. I'm sure that adding this type of information to the
> main oops core/messages would be a good overall goal, instead of only
> having it available to only this one option/user, right?
>
> > Another area where the two approaches have differed has been in
> > handling of network reliability. Historically (though less and less
> > now), we found that we had to transmit data several times. We also
> > used to explicitly space out packets with delays to handle switch chip
> > buffer overruns. Both of these functions I presume could be added to
> > netconsole without too much of a problem.
>
> Yes, I agree netconsole would be good to get this type of change.
>
> > Lastly, this patchset also introduces a 'one-shot' mode, which has
> > saved our bacon several times in the past as well. It's not totally
> > uncommon for the kernel's crash path to be buggy, in turn causing the
> > kernel to emit Oopses until the cows come home (or rather, until the
> > hardware watchdogs trip). One-shot keeps us from emitting too much
> > garbage on the network when this happens.
>
> I thought we had something like "only show the first oops" somewhere in
> the kernel, perhaps I'm just imagining things...
>
> If I am, adding this for all oopses would also be good.
>
> > I hope the above comparison of semantics outlines the motivations we
> > have for not using netconsole and favoring an approach like that used
> > in netoops :)
>
> I think you have just convinced me that you should add this type of
> functionality for all oops messages even more, instead of only doing it
> for your one type of oops transport :)
>
> As for the user/kernel interface, perhaps exporting the data in a text
> format that is "tagged" would be best? Then the whole world can parse
> it easily.

I have been (occasionally) looking at critical kernel messages.
IMO we really need an easy way to find them.

They can begin with any of these strings (and others can be added
too easily):

BUG|panic|MCE|NMI|error:|Oops|Bad|Fatal|Unrecoverable|Unhandled|Weird

We need a simple (single?) tagging method to identify any/all of these,
/methinks.

---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***