lkml.org 
[lkml]   [2012]   [Mar]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: WARNING: Adjusting tsc more then 11%
On Mon, Mar 05, 2012 at 12:24:37PM -0800, John Stultz wrote:
> > > Ok. Well, just to level set: the warning is informative, and points to
> > > unexpected, but not necessarily unsafe behavior.
> > >
> > > In fact, the risk (where mult is adjusted to be large enough to cause an
> > > overflow) we're warning about have been present 2.6.36 or even possibly
> > > before. The change in 3.2 which added the warning also added a more
> > > conservative mult calculation, so we're less likely to get overflow
> > > prone large mult values.
> >
> > Is there a reason you decided to use a WARN_ONCE, which dumps a full stack
> > trace, instead of just printk(KERN_ERR ?
>
> Well, the WARN_ONCE behavior is really nice, since just a printk would
> end up possibly filling the logs, since you might get one every tick.

We have printk_once too.

> > > So it would be great to get further feedback from folks who are seeing
> > > this warning, so we can really hammer this out, but I don't want the
> > > warning spooking anyone into thinking things are terribly broken.
> >
> > Right... people see backtraces and start thinking "my kernel is broken."
> >
> > I'm certainly not meaning to pick on you for this. Lately it seems all
> > the rage to throw WARN_ONs for all kinds of error paths and leave the user
> > to figure out how screwed they are.
>
> Its a trade-off, since we really do want to know if our code has been
> pushed outside of its expected boundaries (either by unexpected hadware
> behavior or by expectations being raised, like long nohz idle times), so
> we have to get folks attention somewhat. The type of error reporting
> Dave's managed to collect here is really great.

It is, yes. Do you know, aside from distro kernel maintainers, how many
reports have you gotten from actual users directly?

> But at the same time, I agree there has been a few cases where the code
> is limited more narrowly then the reality of existing hardware, and we
> end up with a constant stream of error messages that get waved off as
> broken hardware.
>
> There we need to either fix the code or drop the warnings, but I think
> it gets hard when we really want to know about "unexpected behavior,
> except on some wide swath of hardware that always acts poorly", where
> conditionalizing the warnings isn't easy.

Oh my. Quirks in the timekeeping code would just give me nightmares ;).

josh


\
 
 \ /
  Last update: 2012-03-05 21:31    [from the cache]
©2003-2011 Jasper Spaans