On Wed 30-01-13 16:08:27, Andrew Morton wrote:
> On Tue, 29 Jan 2013 15:54:24 +0100
> Jan Kara <j...@suse.cz> wrote:
>
> > > So I was testing the attached patch which does what we discussed. The
> > > bad
> > > news is I was able to trigger a situation (twice) when suddently sda
> > > disappeared and thus all IO requests failed with EIO. There is no trace of
> > > what's happened in the kernel log. I'm guessing that disabled interrupts
> > > on
> > > the printing CPU caused scsi layer to time out for some request and fail
> > > the
> > > device. So where do we go from here?
> > Andrew? I guess this fell off your radar via the "hrm, strange, need to
> > have a closer look later" path?
>
> urgh. I was hoping that if we left it long enough, one of both of us
> would die :(
I'm too young for this strategy to work for me :)
> I fear we will rue the day when we changed printk() to bounce some of
> its work up to a kernel thread.
>
> > Currently I'd be inclined to return to my original solution...
>
> Can we make it smarter? Say, take a peek at the current
> softlockup/nmi-watchdog intervals, work out how for how long we can
> afford to keep interrupts disabled and then use that period and
> sched_clock() to work out if we're getting into trouble? IOW, remove
> the hard-wired "1000" thing which will always be too high or too low
> for all situations.
Yes, I also thought that making offloading more clever (so that offload
doesn't happen unless we really have no choice) could make the approach
more acceptable.
> Implementation-wise, that would probably end up adding a kernel-wide
> function along the lines of
>
> /*
> * Return the maximum number of nanosecond for which interrupts may be
> disabled
> * on the current CPU
> */
> u64 max_interrupt_disabled_duration(void)
> {
> return min(sortirq duration, nmi watchdog duration);
> }
OK, that sounds good. So I'll write some patch...
Honza
--
Jan Kara <j...@suse.cz>
SUSE Labs, CR
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