On Mon, Nov 11, 2013 at 01:44:19PM +0100, Ingo Molnar wrote: > > * Frederic Weisbecker <fweis...@gmail.com> wrote: > > > > That said, I'm not sure what kernel you're running, but there were > > > some issues with time-keeping hereabouts, but more importantly that > > > second timing includes the printk() call of the first -- so that's > > > always going to be fucked. > > > > It's a recent tip:master. So the delta debug printout is certainly > > buggy, meanwhile these lockup only happen with Vince selftests, and they > > trigger a lot of these NMI-too-long issues, or may be that's the other > > way round :)... > > > > I'm trying to narrow down the issue, lets hope the lockup is not > > actually due to printk itself. > > I'd _very_ strongly suggest to not include the printk() overhead in the > execution time delta! What that function wants to report is pure NMI > execution overhead, not problem reporting overhead. > > That way any large number reported there is always a bug somewhere, > somehow.
-ENOPATCH :-) You'll find that there's two levels of measuring NMI latency and the outer will invariably include the reporting of the inner one; fixing that is going to be hideously ugly. That said, I would very strongly suggest to tear that printk() from the NMI path, its just waiting to wreck someone's machine :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
